MACH
Why MACH
MACH (Modern Asynchronous C Hypermedia) is a declarative framework for building asynchronous web applications in C23.
- No build configuration. Compilation, hot reload, and dependency wiring are handled by the framework. There are no build scripts, package managers, or ORMs to set up.
- Memory, concurrency, and I/O managed by the framework. Application code does not call
malloc/freeor manage threads, mutexes, or locks. Database queries run as prepared statements. Pipeline steps emit OpenTelemetry spans, logs, and errors automatically. - Durable tasks and events. Both are persisted. If the process crashes, incomplete tasks resume at the step where they left off and undelivered events replay on the next boot.
- Bundled modules. SSE plus modules for Datastar, HTMX, Tailwind, SQLite, Postgres, MySQL, Redis/Valkey, DuckDB, and auth. Multi-tenant database support is built in.
Table of Contents
Quick Start
Everything runs in Docker; no other local dependencies are required.
mkdir myapp && cd myapp
wget https://docker.nightshadecoder.dev/mach/compose.yml
# Dev server on :3000, telemetry on :4000
# Includes file watching, auto compilation, hot code reloading, HMR
docker compose up
Create main.c with the example below. MACH watches for changes and hot-reloads on save. Use your own editor, or attach to the built-in TUI with docker compose attach mach for an integrated environment with editor, AI, LSP, and console.
#include <mach.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template = "<h1>Hello, world!</h1>")
}
}
}
};
}
The mach() function returns a config struct that defines the application. The home resource maps / to a GET pipeline whose only step renders inline HTML. For a step-by-step walkthrough, see the Guide.
Philosophy
Applications are data transformations: data enters from sources, flows through business logic, and exits to the client. MACH keeps each piece standard. Data comes from raw SQL, HTTP fetch, and JSON rather than ORMs. Business logic is plain C. Output is HTML, CSS, and JS via Mustache templates. These pieces compose inside pipelines: ordered lists of steps that turn a request into a response.
Tooling is also kept standard (lldb for debugging, Playwright and Criterion for testing, OpenTelemetry for observability) and built in.
Everything is a String
The web is largely text: HTTP, HTML, JSON, SQL. MACH takes this literally. The pipeline context stores and passes data as arena-backed strings; there is no intermediate parsing or serialization layer. Request parameters are not parsed into typed structs and objects are not serialized back to JSON. Data flows through the pipeline as strings, interpolated into SQL, templates, and URLs with {{context_key}}.
When business logic needs a specific C type, convert explicitly inside an exec() step.
CLAD
MACH is organized around four principles.
- (C)omposable: small, independent steps chain into feature pipelines.
- (L)ocality of Behavior: the behavior of a unit of code is apparent from reading it. SQL, templates, and behavior for a feature live together rather than across separate model, view, and controller trees.
- (A)utonomous: modules are self-contained: own schemas, migrations, seeds, routes, UI, and logic. The compiler enforces strict boundaries.
- (D)omain Based: each module owns one slice of the app. A
todosmodule defines everything related to todos and nothing else.
CLAD is influenced by:
- Data Oriented Design
- A Philosophy of Software Design
- CUPID
- Self-Contained Systems
- Locality of Behavior
Guide
A walkthrough that builds a working todo app, introducing one MACH concept at a time.
- 1. A Page
- 2. Show Data
- 3. Accept Input
- 4. Handle Errors
- 5. Nested Data
- 6. Tasks
- 7. Modules & Events
- 8. Calling APIs
- 9. External Assets
- 10. Final State
1. A Page
Two resources, each with a GET pipeline. {{url:todos}} resolves to the target resource's URL at render time, so changing a URL pattern updates every link.
#include <mach.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
"<p>Nothing yet.</p>"
"</body></html>"
)
}
}
}
};
}
Each resource names itself ("home", "todos") so other pages reference it by name, not by hard-coded path.
2. Show Data
Add a SQLite database with one migration and one seed, then read from it in the GET pipeline.
#include <mach.h>
+ #include <sqlite.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
+ query({.set_key = "todos", .db = "todos_db",
+ .query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
- "<p>Nothing yet.</p>"
+ "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
"</body></html>"
)
}
}
- }
+ },
+
+ .databases = {{
+ .engine = sqlite_db,
+ .name = "todos_db",
+ .connect = "file:todos.db?mode=rwc",
+ .migrations = {
+ "CREATE TABLE todos ("
+ "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "title TEXT NOT NULL"
+ ");"
+ },
+ .seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
+ }},
+
+ .modules = {sqlite}
};
}
query runs the SELECT and stores the rows under todos in pipeline context. render walks the section with {{#todos}}...{{/todos}}. Migrations run on the first connection.
3. Accept Input
Add a POST verb that validates a title parameter, inserts it, and redirects back to GET (POST-redirect-GET).
#include <mach.h>
#include <sqlite.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
"<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
+ "<form method='post' action='{{url:todos}}'>"
+ "{{csrf:input}}"
+ "<input name='title' value='{{input:title}}'>"
+ "<button>Add</button>"
+ "</form>"
"</body></html>"
)
- }
+ },
+
+ .post = {
+ validate({"title",
+ .validation = validate_not_empty,
+ .message = "title cannot be empty"}),
+ query({.db = "todos_db",
+ .query = "insert into todos(title) values({{title}});"}),
+ redirect("todos")
+ }
}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
};
}
The POST pipeline validates first; on success, the title is promoted from input:title to app scope. The interpolated {{title}} in the SQL is bound as a prepared-statement parameter, not spliced. redirect("todos") returns a 302 to /todos.
{{csrf:input}} emits a hidden input carrying a CSRF token; on POST, MACH automatically verifies that the submitted token matches the one set on the cookie and rejects mismatches with a 403, so every state-changing form needs it.
4. Handle Errors
Validation failure raises http_bad_request. Add a resource-scoped error handler that re-enters the GET pipeline with reroute("todos"), and add error markup to the form template.
#include <mach.h>
#include <sqlite.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
"<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
"<form method='post' action='{{url:todos}}'>"
"{{csrf:input}}"
"<input name='title' value='{{input:title}}'>"
+ "{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
"<button>Add</button>"
"</form>"
"</body></html>"
)
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
redirect("todos")
- }
+ },
+
+ .errors = {
+ {http_bad_request, { reroute("todos") }}
+ }
}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
};
}
reroute("todos") re-enters the GET pipeline in-process, which already knows how to fetch todos and render the page. The input: and error: scopes persist through the reroute, so {{input:title}} repopulates the field and {{#error:title}} renders the message. See redirect & reroute.
5. Nested Data
Add a /todos/:id page that fetches a todo and its comments concurrently, nests the comments inside the todo record, and renders them together. Comments belong to the same domain as todos, so the new comments table is added as a migration on the existing todos_db.
#include <mach.h>
#include <sqlite.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
- "<ul>{{#todos}}<li>{{title}}</li>{{/todos}}</ul>"
+ "<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
"<form method='post' action='{{url:todos}}'>"
"{{csrf:input}}"
"<input name='title' value='{{input:title}}'>"
"{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
"<button>Add</button>"
"</form>"
"</body></html>"
)
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
redirect("todos")
},
.errors = {
{http_bad_request, { reroute("todos") }}
}
- }
+ },
+
+ {"todo", "/todos/:id",
+ .get = {
+ validate({"id", .validation = validate_integer,
+ .message = "must be an integer"}),
+ query(
+ {.set_key = "todo", .db = "todos_db",
+ .query = "select id, title from todos where id = {{id}};"},
+ {.set_key = "comments", .db = "todos_db",
+ .query = "select id, todo_id, body from comments where todo_id = {{id}};"}
+ ),
+ join(
+ .target_table_key = "todo",
+ .target_field_key = "id",
+ .nested_table_key = "comments",
+ .nested_field_key = "todo_id",
+ .target_join_field_key = "comments"
+ ),
+ render(.template =
+ "<html><body>"
+ "{{#todo}}"
+ "<h1>{{title}}</h1>"
+ "<h2>Comments</h2>"
+ "<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
+ "{{/todo}}"
+ "</body></html>"
+ )
+ }
+ }
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
- ");"
+ ");",
+ "CREATE TABLE comments ("
+ "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "todo_id INTEGER NOT NULL REFERENCES todos(id),"
+ "body TEXT NOT NULL"
+ ");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
};
}
The two queries run in parallel under one query() call. join() lifts comments inside each todo record, so the template enters {{#todo}} first and reaches {{#comments}} from within.
6. Tasks
Tasks are named pipelines that run asynchronously on task reactors. Triggered on a cron schedule or enqueued from another pipeline with task("name"). Add a nightly task that records the current todo count into a daily_stats table, and re-run the same task from the POST pipeline so stats stay fresh after every write.
#include <mach.h>
#include <sqlite.h>
config mach(){
return (config) {
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a>"
"</body></html>"
)
}
},
{"todos", "/todos",
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
"<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
"<form method='post' action='{{url:todos}}'>"
"{{csrf:input}}"
"<input name='title' value='{{input:title}}'>"
"{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
"<button>Add</button>"
"</form>"
"</body></html>"
)
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
+ task("record_daily_stats"),
redirect("todos")
},
.errors = {
{http_bad_request, { reroute("todos") }}
}
},
{"todo", "/todos/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
query(
{.set_key = "todo", .db = "todos_db",
.query = "select id, title from todos where id = {{id}};"},
{.set_key = "comments", .db = "todos_db",
.query = "select id, todo_id, body from comments where todo_id = {{id}};"}
),
join(
.target_table_key = "todo",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "todo_id",
.target_join_field_key = "comments"
),
render(.template =
"<html><body>"
"{{#todo}}"
"<h1>{{title}}</h1>"
"<h2>Comments</h2>"
"<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
"{{/todo}}"
"</body></html>"
)
}
}
},
+ .tasks = {
+ {"record_daily_stats", {
+ query({.db = "todos_db",
+ .query = "insert into daily_stats(todo_count) "
+ "select count(*) from todos;"})
+ }, .cron = "0 0 * * *"}
+ },
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"todo_id INTEGER NOT NULL REFERENCES todos(id),"
"body TEXT NOT NULL"
- ");"
+ ");",
+ "CREATE TABLE daily_stats ("
+ "id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,"
+ "todo_count INTEGER NOT NULL"
+ ");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
};
}
The same task definition is reused two ways: .cron = "0 0 * * *" runs it at midnight, and task("record_daily_stats") from the POST pipeline enqueues an on-demand run after each insert. Both invocations land on a task reactor, on separate cores from the request reactors that serve HTTP, so the POST returns immediately. To pass values from the calling context (a user_id, a todo_id), list them under .accepts on the task definition and reference them with {{user_id}} interpolation.
Tasks are durable: MACH checkpoints the context after each step, so a crash mid-task resumes at the failed step on the next boot. See Task Pipelines.
7. Modules & Events
Features/Domains split into modules as the app grows; modules communicate through pub/sub events instead of calling each other directly. A module is a fully self-contained system: its own resources, databases, migrations, context, error and repair handlers, tasks, and event subscribers. main.c composes them and handles cross-cutting concerns.
This step extracts the todos logic into its own module and adds an activity module that logs an entry whenever a todo is created and exposes a page to view the log.
Modules are plain C files. Each defines a function returning config (for example, config todos() { ... }, config activity() { ... }), and main.c pulls them in with #include and registers them under .modules.
Directory layout after this step:
.
├── activity/
│ └── activity.c
├── todos/
│ └── todos.c
└── main.c
main.c: thin root that composes modules and handles cross-cutting concerns.
#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"
config mach(){
return (config){
.resources = {
{"home", "/",
.get = {
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
"<a href='{{url:todos}}'>My Todos</a> · "
"<a href='{{url:activity}}'>Activity</a>"
"</body></html>"
)
}
}
},
.modules = {todos, activity, sqlite}
};
}
todos/todos.c: the todos module, now a publisher.
#include <mach.h>
#include <sqlite.h>
config todos(){
return (config){
.name = "todos",
.publishes = {
{"todo_created", .with = {"title"}}
},
.resources = {
{"todos", "/todos",
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos;"}),
render(.template =
"<html><body>"
"<h1>My Todos</h1>"
"<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>"
"<form method='post' action='{{url:todos}}'>"
"{{csrf:input}}"
"<input name='title' value='{{input:title}}'>"
"{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}"
"<button>Add</button>"
"</form>"
"</body></html>"
)
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({.db = "todos_db",
.query = "insert into todos(title) values({{title}});"}),
task("record_daily_stats"),
emit("todo_created"),
redirect("todos")
},
.errors = {
{http_bad_request, { reroute("todos") }}
}
},
{"todo", "/todos/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
query(
{.set_key = "todo", .db = "todos_db",
.query = "select id, title from todos where id = {{id}};"},
{.set_key = "comments", .db = "todos_db",
.query = "select id, todo_id, body from comments where todo_id = {{id}};"}
),
join(
.target_table_key = "todo",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "todo_id",
.target_join_field_key = "comments"
),
render(.template =
"<html><body>"
"{{#todo}}"
"<h1>{{title}}</h1>"
"<h2>Comments</h2>"
"<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
"{{/todo}}"
"</body></html>"
)
}
}
},
.tasks = {
{"record_daily_stats", {
query({.db = "todos_db",
.query = "insert into daily_stats(todo_count) "
"select count(*) from todos;"})
}, .cron = "0 0 * * *"}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
"CREATE TABLE todos ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"todo_id INTEGER NOT NULL REFERENCES todos(id),"
"body TEXT NOT NULL"
");",
"CREATE TABLE daily_stats ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,"
"todo_count INTEGER NOT NULL"
");"
},
.seeds = {"INSERT INTO todos(title) VALUES('Learn MACH');"}
}},
.modules = {sqlite}
};
}
activity/activity.c: the new subscriber: its own database, its own resource, its own event handler. Nothing references the todos module.
#include <mach.h>
#include <sqlite.h>
config activity(){
return (config){
.name = "activity",
.resources = {
{"activity", "/activity",
.get = {
query({.set_key = "activities", .db = "activity_db",
.query = "select kind, ref, created_at from activities "
"order by created_at desc;"}),
render(.template =
"<html><body>"
"<h1>Activity</h1>"
"<ul>{{#activities}}"
"<li>{{created_at}}: {{kind}}, {{ref}}</li>"
"{{/activities}}</ul>"
"</body></html>"
)
}
}
},
.events = {
{"todo_created", {
query({.db = "activity_db",
.query = "insert into activities(kind, ref) "
"values('created', {{title}});"})
}}
},
.databases = {{
.engine = sqlite_db,
.name = "activity_db",
.connect = "file:activity.db?mode=rwc",
.migrations = {
"CREATE TABLE activities ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"kind TEXT NOT NULL,"
"ref TEXT NOT NULL,"
"created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP"
");"
}
}},
.modules = {sqlite}
};
}
Each module owns one slice of the app. todos owns the todos domain (resources, database, publisher contract, scheduled task); activity owns activity (its resource, database, subscriber). Both can also declare their own context, error and repair handlers, and nested modules. Neither references the other. They only agree on the event name and payload.
When the POST pipeline in todos calls emit("todo_created"), MACH propagates title from the current context to every subscriber's pipeline. The activity module's .events entry runs with title available, writing the row to activity_db. Because .publishes is defined, MACH tracks delivery in a mach_events database, so if the process crashes between emit and delivery the event replays on the next boot. Adding a third subscriber is a new file with an .events entry; the todos module doesn't change.
8. Calling APIs
Pipelines reach external HTTP services the same way they read from databases. fetch() makes one or more requests and stores responses in context; JSON is parsed into tables and records, with nested JSON becoming nested context tables. Multiple items in a single fetch() run concurrently, just like query(). Add a quote of the day and the current weather to the home page, pulled from two public APIs in parallel.
main.c
#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"
config mach(){
return (config){
.resources = {
{"home", "/",
.get = {
+ fetch(
+ {"https://api.quotable.io/random", .set_key = "quote"},
+ {"https://api.weather.dev/now", .set_key = "weather"}
+ ),
render(.template =
"<html><body>"
"<h1>Welcome</h1>"
+ "{{#weather}}"
+ "<p>{{city}}: {{precision:temp_c:0}}°C, {{conditions}}</p>"
+ "{{/weather}}"
+ "{{#quote}}"
+ "<blockquote>{{content}}, {{author}}</blockquote>"
+ "{{/quote}}"
"<a href='{{url:todos}}'>My Todos</a> · "
"<a href='{{url:activity}}'>Activity</a>"
"</body></html>"
)
}
}
},
.modules = {todos, activity, sqlite}
};
}
Both requests run in parallel under one fetch() call, then control passes to render() once both responses are in context. The Quotable API returns {"author": "...", "content": "..."}, which MACH parses into a single-row table under quote; the weather response lands under weather the same way. The template enters each section with {{#quote}} and {{#weather}} to read its fields, the same way it does for query results.
fetch() also supports POST/PUT/PATCH/DELETE, custom headers, JSON or text request bodies, and URLs with {{interpolation}}. See fetch.
9. External Assets
Once templates and SQL grow past a few lines, extract them into files and load them with (asset){ #embed "..." } in .context, then reference them by name from render(), query(), and find(). Each artifact lives in a file named for what it is, edited with native tooling (Mustache-aware HTML editors, SQL formatters), and syntax-highlighted on its own terms. Apply throughout: the root, the todos module, and the activity module.
Directory layout after this step:
.
├── activity/
│ ├── activity.c
│ ├── activity.mustache.html
│ ├── create_activities_table.sql
│ ├── get_activities.sql
│ └── insert_activity.sql
├── static/
│ └── home.mustache.html
├── todos/
│ ├── create_todos_table.sql
│ ├── create_comments_table.sql
│ ├── create_daily_stats_table.sql
│ ├── seed_todos.sql
│ ├── get_todos.sql
│ ├── create_todo.sql
│ ├── get_todo.sql
│ ├── get_comments.sql
│ ├── record_daily_stats.sql
│ ├── todos.c
│ ├── todos_list.mustache.html
│ └── todo_detail.mustache.html
└── main.c
static/ is not a module (no .c file). It's a plain directory for root-level templates that main.c references.
Root
static/home.mustache.html
<html><body>
<h1>Welcome</h1>
{{#weather}}
<p>{{city}}: {{precision:temp_c:0}}°C, {{conditions}}</p>
{{/weather}}
{{#quote}}
<blockquote>{{content}}, {{author}}</blockquote>
{{/quote}}
<a href='{{url:todos}}'>My Todos</a> · <a href='{{url:activity}}'>Activity</a>
</body></html>
main.c: references the home template by name; the fetch() step from the previous section is unchanged.
#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"
config mach(){
return (config){
.resources = {
{"home", "/",
.get = {
fetch(
{"https://api.quotable.io/random", .set_key = "quote"},
{"https://api.weather.dev/now", .set_key = "weather"}
),
render("home")
}
}
},
.context = {
{"home", (asset){
#embed "static/home.mustache.html"
}}
},
.modules = {todos, activity, sqlite}
};
}
Todos module
todos/todos_list.mustache.html
<html><body>
<h1>My Todos</h1>
<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>
<form method='post' action='{{url:todos}}'>
{{csrf:input}}
<input name='title' value='{{input:title}}'>
{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}
<button>Add</button>
</form>
</body></html>
todos/get_todos.sql: and similarly for each other SQL file.
select id, title from todos;
todos/create_todo.sql
insert into todos(title) values({{title}});
SQL {{interpolation}} works the same as inline: bound as prepared parameters, never spliced. Migration files are plain CREATE TABLE statements, one per file. todos/todo_detail.mustache.html holds the detail-page template from step 5.
todos/todos.c: pipelines now reference assets by name; .context lists every asset the module uses.
#include <mach.h>
#include <sqlite.h>
config todos(){
return (config){
.name = "todos",
.publishes = {
{"todo_created", .with = {"title"}}
},
.resources = {
{"todos", "/todos",
.get = {
query({"get_todos", .set_key = "todos", .db = "todos_db"}),
render("todos_list")
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({"create_todo", .db = "todos_db"}),
task("record_daily_stats"),
emit("todo_created"),
redirect("todos")
},
.errors = {
{http_bad_request, { reroute("todos") }}
}
},
{"todo", "/todos/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
query(
{"get_todo", .set_key = "todo", .db = "todos_db"},
{"get_comments", .set_key = "comments", .db = "todos_db"}
),
join(
.target_table_key = "todo",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "todo_id",
.target_join_field_key = "comments"
),
render("todo_detail")
}
}
},
.tasks = {
{"record_daily_stats", {
query({"record_daily_stats", .db = "todos_db"})
}, .cron = "0 0 * * *"}
},
.context = {
{"todos_list", (asset){
#embed "todos_list.mustache.html"
}},
{"todo_detail", (asset){
#embed "todo_detail.mustache.html"
}},
{"get_todos", (asset){
#embed "get_todos.sql"
}},
{"create_todo", (asset){
#embed "create_todo.sql"
}},
{"get_todo", (asset){
#embed "get_todo.sql"
}},
{"get_comments", (asset){
#embed "get_comments.sql"
}},
{"record_daily_stats", (asset){
#embed "record_daily_stats.sql"
}}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
(asset){
#embed "create_todos_table.sql"
},
(asset){
#embed "create_comments_table.sql"
},
(asset){
#embed "create_daily_stats_table.sql"
}
},
.seeds = {
(asset){
#embed "seed_todos.sql"
}
}
}},
.modules = {sqlite}
};
}
Activity module
activity/activity.mustache.html
<html><body>
<h1>Activity</h1>
<ul>{{#activities}}
<li>{{created_at}}: {{kind}}, {{ref}}</li>
{{/activities}}</ul>
</body></html>
activity/insert_activity.sql: the event handler's insert, now a named asset.
insert into activities(kind, ref) values('created', {{title}});
activity/activity.c: same extraction pattern.
#include <mach.h>
#include <sqlite.h>
config activity(){
return (config){
.name = "activity",
.resources = {
{"activity", "/activity",
.get = {
query({"get_activities", .set_key = "activities", .db = "activity_db"}),
render("activity")
}
}
},
.events = {
{"todo_created", {
query({"insert_activity", .db = "activity_db"})
}}
},
.context = {
{"activity", (asset){
#embed "activity.mustache.html"
}},
{"get_activities", (asset){
#embed "get_activities.sql"
}},
{"insert_activity", (asset){
#embed "insert_activity.sql"
}}
},
.databases = {{
.engine = sqlite_db,
.name = "activity_db",
.connect = "file:activity.db?mode=rwc",
.migrations = {
(asset){
#embed "create_activities_table.sql"
}
}
}},
.modules = {sqlite}
};
}
The pipeline shape is unchanged; only where the strings live has moved. Each render(), query(), and find() step takes an asset name as its positional argument; MACH resolves it against .context top-down from the root at boot time (root wins on name conflicts). .migrations and .seeds accept assets directly, which is why entries now read (asset){ #embed "..." } instead of quoted SQL. Templates are still Mustache; SQL still supports {{interpolation}} bound as prepared parameters.
Sharing layout with partials
Each page template above repeats the same <html><body>...</body></html> chrome and its own variant of a top nav. Mustache layout inheritance pulls the shared structure into one template that the others extend.
static/layout.mustache.html: the shared chrome, with a {{$content}} block that child templates override.
<html><body>
<nav>
<a href='{{url:home}}'>Home</a> ·
<a href='{{url:todos}}'>My Todos</a> ·
<a href='{{url:activity}}'>Activity</a>
</nav>
<main>{{$content}}{{/content}}</main>
</body></html>
Register it once at the root so every module can use it.
.context = {
{"home", (asset){
#embed "static/home.mustache.html"
}},
{"layout", (asset){
#embed "static/layout.mustache.html"
}}
}
Each page now extends layout and supplies its own {{$content}}.
static/home.mustache.html
{{<layout}}
{{$content}}
<h1>Welcome</h1>
{{#weather}}
<p>{{city}}: {{precision:temp_c:0}}°C, {{conditions}}</p>
{{/weather}}
{{#quote}}
<blockquote>{{content}}, {{author}}</blockquote>
{{/quote}}
{{/content}}
{{/layout}}
todos/todos_list.mustache.html
{{<layout}}
{{$content}}
<h1>My Todos</h1>
<ul>{{#todos}}<li><a href='{{url:todo:id}}'>{{title}}</a></li>{{/todos}}</ul>
<form method='post' action='{{url:todos}}'>
{{csrf:input}}
<input name='title' value='{{input:title}}'>
{{#error:title}}<span>{{error_message:title}}</span>{{/error:title}}
<button>Add</button>
</form>
{{/content}}
{{/layout}}
{{<layout}}...{{/layout}} says "render the layout asset, but with these overrides." {{$content}}override{{/content}} defines the override for the content block declared in the parent. {{url:todos}} and the section helpers inside the child resolve against the page's pipeline context; the partial inlines the layout's surrounding markup.
For pure inclusion without overrides, use {{>name}} instead. It inlines the named asset rendered against the current scope. This differs from unescaped interpolation ({{{name}}} or {{&name}}): {{>name}} runs Mustache on the asset, so helpers and sections inside it resolve. The unescaped forms emit the value verbatim with no further processing. Use {{>name}} for templates and {{&name}} for already-rendered HTML such as a sanitized blog body.
10. Final State
After all nine concept steps, the project is a small but complete app: a home page with a quote and weather pulled concurrently, a todos module with list and detail pages plus a daily stats cron, and an activity module that subscribes to todo events. Three .c files, two databases, one shared layout.
.
├── todos/ # todos module
│ ├── todos.c # config todos() { resources, db, events, tasks }
│ ├── todos_list.mustache.html # extends layout, lists todos + form
│ ├── todo_detail.mustache.html # one todo with comments
│ ├── create_todos_table.sql # migrations
│ ├── create_comments_table.sql
│ ├── create_daily_stats_table.sql
│ ├── seed_todos.sql # seeds
│ ├── get_todos.sql # queries
│ ├── get_todo.sql
│ ├── get_comments.sql
│ ├── create_todo.sql
│ └── record_daily_stats.sql
├── activity/ # activity module
│ ├── activity.c # config activity() { resource, db, events }
│ ├── activity.mustache.html
│ ├── create_activities_table.sql
│ ├── get_activities.sql
│ └── insert_activity.sql
├── static/ # root-level templates
│ ├── layout.mustache.html # shared chrome with {{$content}} block
│ └── home.mustache.html # home page extending layout
├── public/ # served as-is
│ └── favicon.png
└── main.c # registers modules, declares root resources and context
main.c: registers both modules, defines the home resource, embeds the root templates.
#include <mach.h>
#include <sqlite.h>
#include "todos/todos.c"
#include "activity/activity.c"
config mach(){
return (config){
.resources = {
{"home", "/",
.get = {
fetch(
{"https://api.quotable.io/random", .set_key = "quote"},
{"https://api.weather.dev/now", .set_key = "weather"}
),
render("home")
}
}
},
.context = {
{"home", (asset){
#embed "static/home.mustache.html"
}},
{"layout", (asset){
#embed "static/layout.mustache.html"
}}
},
.modules = {todos, activity, sqlite}
};
}
todos/todos.c: full CRUD on todos, comments via join, validation, error reroute, daily stats cron, publishes todo_created.
#include <mach.h>
#include <sqlite.h>
config todos(){
return (config){
.name = "todos",
.publishes = {
{"todo_created", .with = {"title"}}
},
.resources = {
{"todos", "/todos",
.get = {
query({"get_todos", .set_key = "todos", .db = "todos_db"}),
render("todos_list")
},
.post = {
validate({"title",
.validation = validate_not_empty,
.message = "title cannot be empty"}),
query({"create_todo", .db = "todos_db"}),
task("record_daily_stats"),
emit("todo_created"),
redirect("todos")
},
.errors = {
{http_bad_request, { reroute("todos") }}
}
},
{"todo", "/todos/:id",
.get = {
validate({"id", .validation = validate_integer,
.message = "must be an integer"}),
query(
{"get_todo", .set_key = "todo", .db = "todos_db"},
{"get_comments", .set_key = "comments", .db = "todos_db"}
),
join(
.target_table_key = "todo",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "todo_id",
.target_join_field_key = "comments"
),
render("todo_detail")
}
}
},
.tasks = {
{"record_daily_stats", {
query({"record_daily_stats", .db = "todos_db"})
}, .cron = "0 0 * * *"}
},
.context = {
{"todos_list", (asset){
#embed "todos_list.mustache.html"
}},
{"todo_detail", (asset){
#embed "todo_detail.mustache.html"
}},
{"get_todos", (asset){
#embed "get_todos.sql"
}},
{"create_todo", (asset){
#embed "create_todo.sql"
}},
{"get_todo", (asset){
#embed "get_todo.sql"
}},
{"get_comments", (asset){
#embed "get_comments.sql"
}},
{"record_daily_stats", (asset){
#embed "record_daily_stats.sql"
}}
},
.databases = {{
.engine = sqlite_db,
.name = "todos_db",
.connect = "file:todos.db?mode=rwc",
.migrations = {
(asset){
#embed "create_todos_table.sql"
},
(asset){
#embed "create_comments_table.sql"
},
(asset){
#embed "create_daily_stats_table.sql"
}
},
.seeds = {
(asset){
#embed "seed_todos.sql"
}
}
}},
.modules = {sqlite}
};
}
activity/activity.c: subscribes to todo_created, owns its own database.
#include <mach.h>
#include <sqlite.h>
config activity(){
return (config){
.name = "activity",
.resources = {
{"activity", "/activity",
.get = {
query({"get_activities", .set_key = "activities", .db = "activity_db"}),
render("activity")
}
}
},
.events = {
{"todo_created", {
query({"insert_activity", .db = "activity_db"})
}}
},
.context = {
{"activity", (asset){
#embed "activity.mustache.html"
}},
{"get_activities", (asset){
#embed "get_activities.sql"
}},
{"insert_activity", (asset){
#embed "insert_activity.sql"
}}
},
.databases = {{
.engine = sqlite_db,
.name = "activity_db",
.connect = "file:activity.db?mode=rwc",
.migrations = {
(asset){
#embed "create_activities_table.sql"
}
}
}},
.modules = {sqlite}
};
}
That covers the basic shape of a MACH app: resources route requests, pipelines transform them, error handlers recover, joins compose nested views from separate queries, tasks handle background work, events decouple modules, external assets let templates and SQL live alongside the code that uses them, and fetch() brings in external HTTP data. See Modules & Composition for more on module boundaries.
Reference
Each subsection describes one piece of the framework and lists every option it accepts with a minimal snippet.
- Context
- Databases
- Resource Pipelines
- Template Helpers
- Pipeline Steps
- Imperative API
- Conditionals
- Error and Repair Pipelines
- Event Pipelines
- Task Pipelines
- Modules & Composition
- Module Reference
- Static Files
- External Dependencies
Context
Pipelines read from and write to a shared, scoped key-value store that lives for the duration of one request. Every step draws inputs from context and writes outputs back to it.
.context seeds that store at the root with variables and assets available on every request. Templates and SQL stored here are referenced by name in render(), query(), and find(). Use (asset){ #embed "file" } to bake files into the binary at compile time. Docker secrets exposed to the container are also available in context.
The context uses three scopes: input:xxx for raw request parameters, error:xxx for validation/error data, and unprefixed names for app scope (query results, validated inputs, context variables). validate() bridges input: to app scope.
Inline string value: provide the value directly.
.context = {{"site_name", "MACH App"}}
(asset){ #embed ... }: bake a file into the binary as a named asset.
.context = {
{"layout", (asset){
#embed "layout.mustache.html"
}},
{"get_todos", (asset){
#embed "get_todos.sql"
}}
}
Combined:
.context = {
{"site_name", "MACH App"},
{"version", "1.2.0"},
{"layout", (asset){
#embed "static/layout.mustache.html"
}},
{"home", (asset){
#embed "static/home.mustache.html"
}},
{"get_todos", (asset){
#embed "todos/get_todos.sql"
}},
{"create_todo", (asset){
#embed "todos/create_todo.sql"
}}
}
Databases
Each .databases entry defines a data store. Migrations are forward-only and index-based: they run in array order, each applied once, with new migrations appended to the end. Seeds are idempotent and safe to re-run. Both are tracked in a mach_meta table.
Multi-tenant databases use {{interpolation}} in .connect. Connections are pooled with LRU eviction: active tenants stay warm, idle connections are reclaimed.
.engine: database engine constant, provided by a module.
.engine = sqlite_db
.name: identifier referenced by .db in query() and find().
.name = "todos_db"
.connect: engine-specific connection string. Supports {{interpolation}} for multi-tenancy.
.connect = "file:{{user_id}}_todo.db?mode=rwc"
.migrations: array of SQL migration strings or assets, applied once each in order.
.migrations = {
(asset){
#embed "create_todos_table.sql"
}
}
.seeds: array of idempotent seed statements, safe to re-run on every boot.
.seeds = {"INSERT OR IGNORE INTO todos(id, title) VALUES(1, 'Hello');"}
Combined:
.databases = {{
.engine = sqlite_db,
.name = "blog_db",
.connect = "file:{{user_id}}_blog.db?mode=rwc",
.migrations = {
"CREATE TABLE blogs ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL,"
"content TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"blog_id INTEGER NOT NULL REFERENCES blogs(id),"
"body TEXT NOT NULL"
");"
},
.seeds = {
"INSERT OR IGNORE INTO blogs(id, title, content) VALUES(1, 'Hello', 'First post');"
}
}}
Engines: sqlite_db, postgres_db, mysql_db, redis_db, duckdb_db
Resource Pipelines
MACH is resource-based, not route-based. Each entry in .resources defines a named URL endpoint with HTTP verb pipelines. Resources are identified by name: {{url:name}}, redirect(), and reroute() take a name[:arg1:arg2...] identifier; positional args fill the :params of the URL pattern in order. Path specificity is automatic: exact matches (/todos/active) beat parameterized matches (/todos/:id) regardless of definition order.
{{url:name}}with URL params. Args after the name are positional, colon-separated, literals or context keys:
- ✅
{{url:todo:5}}resolves to/todos/5- ✅
{{url:todo:id}}readsidfrom current scope (useful inside{{#todos}}...{{/todos}}where each iteration has its ownid)- ✅
{{url:org_todo:acme:5}}fills multiple:paramsin URL-pattern order (e.g./orgs/:org/todos/:id)
Clients select a verb via the request method, or by passing http_method as a query/form parameter. This lets HTML forms (limited to GET/POST) reach any verb, and gives SSE a connection path: /todos?http_method=sse.
.name (pos): resource identifier used by {{url:name}}, redirect(), and reroute().
{"todos", "/todos", .get = { ... }}
.url (pos): URL pattern. Supports :params.
{"todo", "/todos/:id", .get = { ... }}
.steps (pos): shared steps that run before every verb pipeline on the resource.
{"todo", "/todos/:id", {
validate({"id", .validation = "^\\d+$", .message = "must be a number"})
}, .get = { ... }, .delete = { ... }}
.mime: default response content type for the resource.
{"feed", "/feed.json", .mime = mime_json, .get = { ... }}
.get .post .put .patch .delete: verb pipelines: ordered arrays of steps that transform a request into a response.
{"todos", "/todos",
.get = { query({"get_todos", .set_key = "todos", .db = "db"}), render("todos") },
.post = { validate({"title", .validation = validate_not_empty}), redirect("todos") }
}
.sse: persistent SSE channel. First positional is the channel name; steps run on connect.
{"todos", "/todos",
.sse = {"todos/{{user_id}}",
query({"get_todos", .set_key = "todos", .db = "db"}),
sse(.event = "initial", .data = {"{{todos}}"})
}
}
.errors / .repairs: resource-scoped error and repair pipelines. See Error and Repair Pipelines.
{"todos", "/todos",
.post = { ... },
.errors = {{http_bad_request, { render("form") }}}
}
Combined:
{"todo", "/todos/:id", {
validate({"id", .validation = "^\\d+$", .message = "must be a number"})
},
.mime = mime_html,
.get = { find({"get_todo", .set_key = "todo", .db = "todos_db"}),
render("todo") },
.patch = { validate({"title", .validation = validate_not_empty, .message = "required"}),
query({.db = "todos_db",
.query = "update todos set title = {{title}} where id = {{id}};"}),
redirect("todo:{{id}}") },
.delete = { query({.db = "todos_db",
.query = "delete from todos where id = {{id}};"}),
redirect("todos") },
.sse = {"todo/{{id}}", sse(.event = "ready") },
.errors = {{http_not_found, { render("404") }}}
}
MIME types (for .mime): mime_html, mime_txt, mime_sse, mime_json, mime_js
Template Helpers
Templates are Mustache. MACH supports the full Mustache base spec with one exception: dot notation. Use a section instead. {{a.b}} does not work; {{#a}}{{b}}{{/a}} does.
Supported base-spec features:
- Interpolation:
{{name}}(HTML-escaped),{{{name}}}or{{&name}}(unescaped). - Sections:
{{#name}}...{{/name}}renders when truthy and iterates over arrays. - Inverted sections:
{{^name}}...{{/name}}renders when falsy or empty. - Comments:
{{! ignored }}. - Set delimiters:
{{=<% %>=}}. - Partials:
{{>name}}inlines the context asset namedname, rendered against the current scope. - Layout inheritance:
{{<parent}}{{$block}}override{{/block}}{{/parent}}rendersparentwith each{{$block}}default{{/block}}block in the parent replaced by the override here.
No Mustache extensions are supported. There are no lambdas, no {{#if}} / {{else}}, no {{#each}}. Branching and iteration come from sections; counts and conditions are computed in SQL or exec() and rendered as plain context values.
On top of base Mustache, templates and other interpolated strings support built-in helpers with {{helper:args}} syntax. Arguments are positional and colon-separated; each can be a literal or a context key.
{{precision:field:N}}: format a numeric value with N decimal places.
render(.template = "<p>Total: ${{precision:total:2}}</p>")
{{input:field}}: raw, unvalidated request parameter from the input scope. Typically used to repopulate form fields after a validation error.
render(.template = "<input name='title' value='{{input:title}}'>")
{{error:field}}: truthy when field has an error. Used as a Mustache section to conditionally render markup.
render(.template = "{{#error:title}}<span class='error'>invalid</span>{{/error:title}}")
{{error_message:field}}: human-readable message for a field error, from validate()'s .message or from error_set().
render(.template = "<span>{{error_message:title}}</span>")
{{error_code:field}}: HTTP status code associated with a field error (e.g. 400, 404).
render(.template = "<p>Code: {{error_code:title}}</p>")
{{url:name}}: resolve a resource identifier to its URL. Takes positional args to fill :params. Args can be literals or context keys.
render(.template =
"<a href='{{url:todos}}'>All</a>" // /todos
"<a href='{{url:todo:5}}'>Item 5</a>" // /todos/5
"<a href='{{url:todo:id}}'>From context</a>" // /todos/{{id}}
)
{{asset:filename}}: resolve a file in public/ to a cache-busted URL (content checksum + immutable cache headers). See Static Files.
render(.template = "<link rel='stylesheet' href='{{asset:styles.css}}'>")
{{csrf:token}}: emit a CSRF token, for use in URL query strings. Generates a random hash, sets it on an httponly/secure/samesite cookie, and outputs the same value inline.
render(.template = "<a href='{{url:logout}}?csrf={{csrf:token}}'>Log out</a>")
{{csrf:input}}: emit a hidden <input> carrying a CSRF token, for use inside a <form>. Same cookie-setting behavior as {{csrf:token}}.
render(.template = "<form>{{csrf:input}}<input name='title'><button>Add</button></form>")
Combined:
render(.template =
"<link rel='stylesheet' href='{{asset:styles.css}}'>"
"<article>"
"{{#post}}"
"<h2>{{title}}</h2>"
"<p>Rating: {{precision:score:1}}/5</p>"
"<div>{{&body_html}}</div>"
"{{/post}}"
"<form method='post' action='{{url:comments}}'>"
"{{csrf:input}}"
"<input name='body' value='{{input:body}}'>"
"{{#error:body}}<span>{{error_message:body}}</span>{{/error:body}}"
"<button>Comment</button>"
"</form>"
"<a href='{{url:logout}}?csrf={{csrf:token}}'>Log out</a>"
"</article>"
)
CSRF verification is automatic. MACH checks that the incoming token (from the form field or query parameter) matches the value stored in the CSRF cookie and rejects mismatches with a 403. The cookie is httponly, secure, and samesite, so nothing beyond emitting
{{csrf:token}}or{{csrf:input}}in the rendered response is required.
Pipeline Steps
Steps are the units of work in a pipeline. Each receives the current context, acts on it, and passes control to the next. All steps accept .if_context and .unless_context for conditional execution.
- validate
- find & query
- join
- fetch
- exec
- emit
- task
- sse
- render
- headers & cookies
- redirect & reroute
- nest
validate
Checks request parameters (query string, form body, URL params) against regex patterns. On success, each value is promoted from input:name to app scope. On failure, errors land in error:name and a 400 Bad Request triggers the nearest error/repair pipeline. All validations in one call complete before the error fires, so all errors are available together for form re-rendering.
Built-in regex macros are defined in mach.h; define your own the same way: #define validate_zipcode "^\\d{5}$".
.param_key (pos): name of the parameter to validate.
validate({"title", .validation = "^\\S+$", .message = "required"})
.validation: regex pattern, or a built-in validator macro.
validate({"email", .validation = validate_email, .message = "bad email"})
.message: human-readable error shown via {{error_message:name}}.
validate({"age", .validation = "^\\d+$", .message = "must be a number"})
.optional: skip validation when the parameter is absent.
validate({"filter", .optional = true, .validation = "^(active|done)$"})
.fallback: default value injected when the parameter is absent.
validate({"page", .fallback = "1", .validation = "^\\d+$"})
Combined:
validate(
{"email", .validation = validate_email, .message = "must be a valid email"},
{"title", .validation = validate_not_empty, .message = "cannot be empty"},
{"page", .fallback = "1",
.validation = "^\\d+$", .message = "must be a number"},
{"filter", .optional = true,
.validation = "^(active|done)$", .message = "must be 'active' or 'done'"}
)
Built-in validators:
- Strings:
validate_not_empty,validate_alpha,validate_alphanumeric,validate_slug,validate_no_html - Numbers:
validate_integer,validate_positive,validate_float,validate_percentage - Identity:
validate_email,validate_uuid,validate_username - Dates & times:
validate_date,validate_time,validate_datetime - Web:
validate_url,validate_ipv4,validate_hex_color - Codes:
validate_zipcode_us,validate_phone_e164,validate_cron - Security:
validate_no_sqli,validate_token,validate_base64 - Boolean:
validate_boolean,validate_yes_no,validate_on_off
find & query
Both run database queries. .db selects the database; .set_key stores the result in context as a table, even for single-row queries. SQL is either inlined with .query or referenced by name as the positional (loaded from .context). Multiple items in a single step run concurrently. Queries use prepared statements; interpolated {{values}} are bound, not spliced. For transactions, use BEGIN/COMMIT/ROLLBACK directly in your queries.
The only difference between the two: find() raises 404 Not Found on zero rows; query() does not.
Positional asset name OR
.query, not both. Each item picks one:
- ✅
query({"get_todos", .set_key = "todos", .db = "todos_db"}): SQL loaded by asset name from.context- ✅
query({.set_key = "todos", .db = "todos_db", .query = "select id, title from todos;"}): SQL inlined- ❌
query({"get_todos", .set_key = "todos", .db = "todos_db", .query = "select ..."}): combining the two is rejected
Concurrency = multiple items in one step, not multiple steps.
query({...}, {...})runs both queries in parallel. Two back-to-backquery({...})steps run serially.
.template_key (pos): name of a SQL asset stored in .context. Mutually exclusive with .query.
query({"get_todos", .set_key = "todos", .db = "todos_db"})
.query: inline SQL string. Supports {{interpolation}}, bound as parameters. Mutually exclusive with the positional asset name.
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos where user_id = {{user_id}};"})
.set_key: context key for the result table.
query({.set_key = "active", .db = "db", .query = "select * from todos;"})
.db: name of the database, matching a .databases entry.
query({.db = "todos_db", .query = "select 1;"})
.if_context / .unless_context (per item): conditionally include or skip individual queries while running the others concurrently.
query(
{"get_todos", .set_key = "todos", .db = "db"},
{"get_urgent", .if_context = "show_urgent", .set_key = "u", .db = "db"}
)
Combined:
query(
{"get_todos", .set_key = "todos", .db = "todos_db"},
{.set_key = "count", .db = "todos_db",
.query = "select count(*) as n from todos where user_id = {{user_id}};"},
{.if_context = "show_urgent", .set_key = "urgent", .db = "todos_db",
.query = "select id, title from todos where user_id = {{user_id}} and priority = 'high';"}
)
join
Nests records from one context table into each matching record of another, like a SQL JOIN performed in memory. Useful when records come from separate databases or queries and need to be combined. After the step, each outer record gains a new field holding its matched inner records.
.target_table_key: outer table whose records receive nested children.
.target_table_key = "projects"
.target_field_key: field on the outer table to match against.
.target_field_key = "id"
.nested_table_key: inner table whose records get nested.
.nested_table_key = "todos"
.nested_field_key: field on the inner table that points at the outer.
.nested_field_key = "project_id"
.target_join_field_key: new field on outer records holding the matched inner records.
.target_join_field_key = "todos"
Combined:
join(
.target_table_key = "projects",
.target_field_key = "id",
.nested_table_key = "todos",
.nested_field_key = "project_id",
.target_join_field_key = "todos"
)
Full context example. A common pattern is concurrent query() → join() → render(): fetch parent and children from separate queries, then render them as one nested structure. Blog + comments, single database:
{"blog", "/blogs/:id",
.get = {
validate({"id", .validation = validate_integer, .message = "must be an integer"}),
// Fetch both concurrently: one query() call, two items
query(
{.set_key = "blog", .db = "blog_db",
.query = "select id, title, content from blogs where id = {{id}};"},
{.set_key = "comments", .db = "blog_db",
.query = "select id, blog_id, body from comments where blog_id = {{id}};"}
),
// Nest each comment into its matching blog record
join(
.target_table_key = "blog",
.target_field_key = "id",
.nested_table_key = "comments",
.nested_field_key = "blog_id",
.target_join_field_key = "comments"
),
// Enter {{#blog}} first; after join(), comments lives INSIDE each blog record
render(.template =
"<article>"
"{{#blog}}"
"<h1>{{title}}</h1>"
"<div>{{content}}</div>"
"<h2>Comments</h2>"
"<ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>"
"{{/blog}}"
"</article>"
)
}
}
Shape of the context at each step:
after query(): { blog: [{id, title, content}],
comments: [{id, blog_id, body}, ...] } // two sibling tables
after join(): { blog: [{id, title, content,
comments: [{id, blog_id, body}, ...]}] } // nested inside blog
fetch
Makes one or more HTTP requests and stores responses in context. JSON is parsed into tables and records (with nested tables for nested JSON); plain-text responses are stored as a string. Like query(), multiple items in a single step run concurrently, so a page can fan out to several services in parallel and join the results downstream.
Concurrency = multiple items in one step, not multiple steps.
fetch({...}, {...})runs both requests in parallel. Two back-to-backfetch({...})steps run serially.
.url (pos): request URL; supports {{interpolation}}.
fetch({"https://api.weather.dev/forecast?city={{city}}", .set_key = "w"})
.set_key: context key for the response.
fetch({"https://api.weather.dev/now", .set_key = "weather"})
.method: HTTP method. Defaults to http_get.
fetch({"https://api.dev/charge", .set_key = "r", .method = http_post})
.headers: array of name/value pairs.
fetch({"https://api.dev/me", .set_key = "r",
.headers = {{"Authorization", "Bearer {{token}}"}}})
.json: context key serialized as the JSON request body.
fetch({"https://api.dev/charge", .set_key = "receipt",
.method = http_post, .json = "order"})
.text: context key sent as the plain-text request body.
fetch({"https://api.dev/log", .set_key = "r",
.method = http_post, .text = "raw_body"})
.if_context / .unless_context (per item): conditionally include or skip individual requests while running the others concurrently.
fetch(
{"https://api.weather.dev/now", .set_key = "weather"},
{"https://api.quotes.dev/random", .if_context = "show_quote", .set_key = "quote"}
)
Combined, single request:
fetch({"https://api.payments.dev/charge",
.set_key = "receipt",
.method = http_post,
.headers = {
{"Authorization", "Bearer {{api_key}}"},
{"Idempotency-Key", "{{order_id}}"}
},
.json = "order"
})
Combined, concurrent fan-out:
fetch(
{"https://api.weather.dev/now?city={{city}}", .set_key = "weather"},
{"https://api.news.dev/headlines?topic={{topic}}", .set_key = "news"},
{"https://api.quotes.dev/random", .set_key = "quote"}
)
HTTP methods (for .method): http_get, http_post, http_put, http_patch, http_delete, http_sse_method
exec
Calls a C function or block with access to the context via the Imperative API. exec() is where business logic and data shaping lives: enriching query results with computed fields, aggregating across rows, transforming data between steps, calling external C libraries, blocking I/O, CPU-heavy work. Execution is dispatched to the shared thread pool, which releases the reactor; the pipeline resumes on the original reactor when the call returns. To trigger an error/repair pipeline from inside, call error_set().
Block (pos): inline block, for short logic specific to this pipeline. Here, attaching each challenger's opponent id so the template can render two voting forms with the right winner/loser pairing:
exec(^(){
auto t = get("challengers");
record_set(table_get(t, 0), "opponent_id",
record_get(table_get(t, 1), "id"));
record_set(table_get(t, 1), "opponent_id",
record_get(table_get(t, 0), "id"));
})
.call: reference to a named C function, for logic reuse across pipelines.
exec(.call = assign_opponents)
Inside exec blocks and functions, context, memory, errors, tables, and records are manipulated through the Imperative API.
emit
Triggers an internal pub/sub event. Subscribers in other modules react in their .events pipelines, with no direct dependency on the emitter. See Event Pipelines.
Event name (pos): name of the event to publish.
emit("todo_created")
task
Adds a named job to the task database; the calling pipeline continues immediately. Task reactors pick up queued jobs and execute their pipelines. See Task Pipelines.
Task name (pos): name of a task defined in .tasks.
task("recount_todos")
sse
Pushes a Server-Sent Event. With .channel, the event is broadcast to all clients on that channel. Without .channel, the event is returned directly to the requesting client. See Resource Pipelines.
.channel (pos): channel to broadcast on; supports {{interpolation}}.
sse(.channel = "todos/{{user_id}}", .event = "new_todo", .data = {"{{todo}}"})
.event: SSE event: line value.
sse(.event = "ping")
.data: array of strings, one per SSE data: line (multi-line data).
sse(.event = "msg", .data = {"line one", "line two"})
.comment: SSE : comment line value, useful for keep-alives.
sse(.comment = "keep-alive")
Combined:
sse(
.channel = "todos/{{user_id}}",
.event = "todo_updated",
.data = {"id: {{todo_id}}", "title: {{title}}"},
.comment = "broadcast at {{timestamp}}"
)
render
Outputs a template using the current context. Templates are referenced by name from .context or inlined.
.template_key (pos): asset name in .context. The asset is a template.
render("todos")
.template: inline template string.
render(.template = "<h1>{{site_name}}</h1>") // {{site_name}} from .context
.status: HTTP response status (defaults to http_ok).
render("not_found", .status = http_not_found)
.mime: override the response content type.
render("plain", .mime = mime_txt)
.engine: template engine. Accepts mustache (default) or mdm for Markdown-with-Mustache. Additional engined can be added with modules.
render(.engine = mdm, .template = "# Welcome, {{user_name}}")
.json_table_key: context table to serialize as the JSON response. Sets application/json; nested tables produce nested JSON.
render(.json_table_key = "todos")
HTTP statuses (for .status): http_ok (200), http_created (201), http_redirect (302), http_bad_request (400), http_not_authorized (401), http_not_found (404), http_error (500)
MIME types (for .mime): mime_html, mime_txt, mime_sse, mime_json, mime_js
headers & cookies
Set HTTP response headers and cookies declaratively. Both accept an array of name/value pairs; values support {{interpolation}}.
Pairs (pos): array of {name, value} entries.
headers({{"X-Request-Id", "{{request_id}}"}})
cookies({{"session", "{{session_id}}"}})
Combined:
headers({
{"X-Request-Id", "{{request_id}}"},
{"Cache-Control", "no-store"}
}),
cookies({
{"session", "{{session_id}}"},
{"theme", "{{theme}}"}
})
redirect & reroute
redirect() returns a 302 to the client, causing the browser to navigate. reroute() re-enters the router server-side, executing another resource's pipeline within the same request. Both take a resource identifier in the same name[:arg1:arg2...] format as {{url:name}}: colon-separated positional args that fill the target's :params. Args can be literals or context keys, and support {{interpolation}}.
Resource identifier (pos): target resource name, plus positional args for any :params.
redirect("todos") // 302 to /todos (bare resource, no args)
redirect("todo:5") // 302 to /todos/5 (literal id)
redirect("todo:{{id}}") // 302 to /todos/5 (id from context)
redirect("org_todo:acme:5") // 302 to /orgs/acme/todos/5 (multi-arg)
reroute("todo:{{id}}") // run that pipeline in-process
nest
Groups multiple steps into a single composite step. Useful when applying one .if_context/.unless_context to several steps, to avoid repeating the condition on each.
.steps (pos): array of steps that run as a unit.
nest({query({...}), emit("urgent_todo"), render("urgent")})
.if_context / .unless_context: condition applied to the whole group.
nest({query({...}), emit("urgent_todo"), render("urgent")},
.if_context = "is_urgent")
Imperative API
Functions called from exec() blocks and .call functions to read and write context, allocate memory, raise errors, and manipulate tables and records.
context
Read, write, and test context keys, and resolve {{interpolation}} against the current scope.
get(name): returns the value stored under name, or nullptr if absent. The returned pointer is whatever was stored: a string for scalars, a table for query and fetch results.
auto todos = get("todos");
set(name, value): writes value to name, exposing it to downstream steps and to templates.
set("is_urgent", "1");
has(name): returns true when name exists in the current scope.
if (has("user_id")) { ... }
format(fmt): returns fmt with {{name}} interpolations resolved against the current context. Same scopes and helpers as templates.
string greeting = format("Hello, {{user_name}}");
Combined:
exec(^(){
auto rows = get("todos");
if (table_count(rows) > 5) {
set("is_urgent", "1");
set("banner", format("{{user_name}} has more than 5 open todos"));
}
})
memory
Pipeline-arena allocation and deferred cleanup of foreign pointers. Both clear when the request completes.
allocate(bytes): returns a buffer from the pipeline arena. Reclaimed automatically on request completion.
char *buf = allocate(256);
defer_free(ptr): schedules free() for a pointer returned by an external library. Runs when the arena is released.
char *out = third_party_alloc(256);
defer_free(out);
Combined:
exec(^(){
char *url = allocate(512);
build_signed_url(url, 512, get("path"));
set("signed_url", url);
char *raw = third_party_render_md(get("markdown"));
defer_free(raw);
set("html", raw);
})
errors
Raise field-scoped errors from inside exec() to trigger error/repair pipelines. The keys land in the error:name scope, visible to templates as {{error:name}}, {{error_code:name}}, and {{error_message:name}}.
error_set(name, err): associates an error with name and triggers the nearest error or repair pipeline.
error_set("token", (error){ http_bad_request, "token has expired" });
error_get(name): returns the error previously set on name.
error e = error_get("token");
error_has(name): returns true when name has an error.
if (error_has("token")) { ... }
Combined:
exec(^(){
string token = get("token");
if (!token || strlen(token) < 16) {
error_set("token", (error){
http_bad_request,
"token must be at least 16 characters"
});
}
})
tables
Tables are ordered collections of records, the shape query() produces and fetch() parses JSON into. Use these to build derived results.
table_new(): returns an empty table in the pipeline arena.
table t = table_new();
table_count(t): number of records in t.
int n = table_count(get("todos"));
table_get(t, i): record at index i, or nullptr if out of range.
record first = table_get(get("todos"), 0);
table_add(t, r): appends r to t.
table_add(t, record_new());
table_remove(t, r): removes record r from t.
table_remove(t, r);
table_remove_at(t, i): removes the record at index i.
table_remove_at(t, 0);
Combined:
exec(^(){
table source = get("raw_users");
table active = table_new();
for (int i = 0; i < table_count(source); i++) {
record u = table_get(source, i);
string status = record_get(u, "status");
if (status && strcmp(status, "active") == 0) {
table_add(active, u);
}
}
set("active_users", active);
})
records
Records are name-value bags, the shape of one row from query() or one object from fetch(). All values are strings, in keeping with Everything is a String.
record_new(): returns an empty record in the pipeline arena.
record r = record_new();
record_get(r, name): string value of name, or nullptr if absent.
string title = record_get(r, "title");
record_set(r, name, value): writes value to name on r.
record_set(r, "title", "New title");
record_remove(r, name): removes name from r.
record_remove(r, "draft");
Combined:
exec(^(){
table todos = get("todos");
for (int i = 0; i < table_count(todos); i++) {
record t = table_get(todos, i);
string title = record_get(t, "title");
if (title && strlen(title) > 40) {
record_set(t, "is_long", "1");
}
}
})
Conditionals
Every step accepts .if_context and .unless_context, which name a context variable. They work for any context value: validated inputs, query results, framework flags such as is_htmx, or flags set from exec().
.if_context: context key. Step runs only when the value is present.
render("fragment", .if_context = "is_htmx")
.unless_context: context key. Step runs only when the value is absent.
render("full_page", .unless_context = "is_htmx")
For multi-state branching, set context flags from exec(), then key downstream steps off them:
exec(.call = classify_todo),
render("urgent_confirmation", .if_context = "is_urgent"),
render("standard_confirmation", .unless_context = "is_urgent")
Error and Repair Pipelines
When a pipeline step fails, execution halts and MACH searches for a handler bottom-up: resource, then module, then root. Errors are terminal: the handler sends a response and ends the request. Repairs are resumable: they fix the context and resume the original pipeline at the step after the failure. If no matching repair is found, resolution falls through to errors. Unhandled errors fall through to MACH's internal handler, which renders the error message as text/plain with the error code as the HTTP status, and surfaces in the TUI console and telemetry.
The error scope is shared across validate() failures and error_set() calls: {{error:name}}, {{error_code:name}}, {{error_message:name}}. The raw input value remains available in input:name for re-rendering forms.
.errors: terminal handlers keyed by error code.
.errors = {
{http_not_found, { render("404") }},
{http_bad_request, { render("form") }}
}
.repairs: resumable handlers keyed by error code.
.repairs = {
{http_not_authorized, { exec(.call = refresh_session_token) }}
}
Combined:
.errors = {
{http_not_found, { render("404") }},
{http_bad_request, { render("form") }},
{http_error, { render("500") }}
},
.repairs = {
{http_not_authorized, { exec(.call = refresh_session_token) }}
}
Built-in error codes: http_ok (200), http_created (201), http_redirect (302), http_bad_request (400), http_not_authorized (401), http_not_found (404), http_error (500). Any integer works; the http_* constants are convenience names. Define your own for domain-specific errors, e.g. #define err_quota_exceeded 723.
Event Pipelines
Internal pub/sub for cross-module communication. The publisher does not know who listens; the subscriber does not know who emits. Adding a subscriber means adding a new module with an .events entry, with no changes to the publisher.
Events are durable by default. When .publishes is defined anywhere in the app, MACH creates a mach_events database to track delivery. If the process crashes, undelivered events are replayed on the next boot.
.publishes: outbound event contracts. .event is the name; .with lists context keys to pass along.
.publishes = {
{"todo_created", .with = {"user_id", "title"}}
}
.events: subscriber pipelines keyed by event name.
.events = {
{"todo_created", {
query({"insert_activity", .db = "activity_db"})
}}
}
.errors / .repairs (per subscriber): each .events entry can declare its own handlers, resolved with the same bottom-up search as resource pipelines. See Error and Repair Pipelines.
.events = {
{"todo_created", {
query({"insert_activity", .db = "activity_db"})
}, .errors = {{http_error, { exec(.call = log_subscriber_failure) }}}}
}
Combined:
// todos/todos.c: publisher
config todos(){
return (config){
.name = "todos",
.publishes = {
{"todo_created", .with = {"user_id", "title"}},
{"todo_deleted", .with = {"user_id", "todo_id"}}
},
.resources = {
{"todos", "/todos",
.post = {
validate({"title", .validation = validate_not_empty}),
query({"insert_todo", .db = "todos_db"}),
emit("todo_created"),
redirect("todos")
}
}
}
};
}
// activity/activity.c: subscriber
config activity(){
return (config){
.name = "activity",
.events = {
{"todo_created", {
query({.db = "activity_db",
.query = "insert into activities(kind, user_id, ref) "
"values('created', {{user_id}}, {{title}});"})
}},
{"todo_deleted", {
query({.db = "activity_db",
.query = "insert into activities(kind, user_id, ref) "
"values('deleted', {{user_id}}, {{todo_id}});"})
}}
}
};
}
Task Pipelines
Tasks are named pipelines that run asynchronously on task reactors. Fire-and-forget: the calling pipeline continues immediately. Defined at the module or root level. Triggered on demand with task("name") or on a schedule via .cron. Tasks can enqueue more tasks via task().
Tasks are durable: when .tasks is defined, MACH creates a mach_tasks database and checkpoints the context after each step. A crash mid-task resumes at the step where it left off on the next boot.
.name (pos): task identifier, called via task("name").
.tasks = {
{"recount_todos", { query({.db = "db", .query = "update users set ..."}) }}
}
.accepts: context keys to pull from the caller into the task.
{"recount_todos", {
query({.db = "db", .query = "update users set todo_count = ... where id = {{user_id}};"})
}, .accepts = {"user_id"}}
.cron: standard cron schedule for recurring tasks (no caller required).
{"daily_digest", {
query({.db = "db", .query = "insert into digest_reports ..."})
}, .cron = "0 8 * * *"}
Steps (pos): the task's pipeline body, the second positional brace block, before any designated fields.
{"name", { query({...}), emit("done"), task("followup") }, .accepts = {...}}
.errors / .repairs (per task): each task can declare its own handlers, resolved with the same bottom-up search as resource pipelines. See Error and Repair Pipelines.
{"send_invoice", {
fetch({"https://api.billing.dev/invoices/{{invoice_id}}", .set_key = "inv"})
}, .repairs = {{http_not_authorized, { exec(.call = refresh_billing_token) }}}}
Combined:
.tasks = {
// on-demand: enqueued via task("recount_todos")
{"recount_todos", {
query({.db = "todos_db",
.query = "update users set todo_count = "
"(select count(*) from todos where user_id = users.id) "
"where id = {{user_id}};"})
}, .accepts = {"user_id"}},
// recurring: runs on schedule, no caller
{"daily_digest", {
query({.db = "todos_db",
.query = "insert into digest_reports(generated_at) values(now());"}),
emit("digest_ready")
}, .cron = "0 8 * * *"}
}
Modules & Composition
Every MACH app and module returns a config struct. The root main.c must define a function named mach(); modules define their own functions with any name and register them in .modules by bare function reference. A module owns its own resources, databases, migrations, templates, and event contracts.
When the root and a module both define something with the same name, resolution depends on the kind. Context variables and databases resolve top-down from the root, so the root wins. Error and repair handlers resolve bottom-up from the resource (resource → module → root), so the innermost handler wins. Modules don't call each other directly; they communicate through pub/sub events.
.name: module identifier.
config todos(){ return (config){ .name = "todos", /* resources, databases, ... */ }; }
.modules: other modules to compose into this one (root or nested).
.modules = {todos, activity, sqlite, session_auth}
Complete module file. A module returns a config with the same shape as the root app (.resources, .databases, .events, etc.), plus a .name for identity. Resource fields like .url, .mime, .get are not top-level config fields; they belong inside entries of .resources. A blogs/blogs.c:
#include <mach.h>
#include <sqlite.h>
config blogs(){
return (config){
.name = "blogs",
.resources = {
{"blog", "/blogs/:id",
.get = { /* validate → query → join → render; see `join` worked example */ }
}
},
.databases = {{
.engine = sqlite_db,
.name = "blog_db",
.connect = "file:blogs.db?mode=rwc",
.migrations = {
"CREATE TABLE blogs ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"title TEXT NOT NULL,"
"content TEXT NOT NULL"
");",
"CREATE TABLE comments ("
"id INTEGER PRIMARY KEY AUTOINCREMENT,"
"blog_id INTEGER NOT NULL REFERENCES blogs(id),"
"body TEXT NOT NULL"
");"
}
}}
};
}
Bring the module into scope by #includeing its .c file from main.c, then register it with .modules = {blogs, sqlite}. The module's resources and databases are merged into the app tree at registration.
// main.c
#include <mach.h>
#include "blogs/blogs.c"
config mach(){ return (config){ .modules = {blogs, sqlite} }; }
A typical project layout:
├── todos/ # todos module
│ ├── todos.c # config todos() { ... }
│ ├── todos.mustache.html
│ ├── create_todos_table.sql
│ └── get_todos.sql
├── activity/ # activity module
│ └── activity.c
├── static/ # root-level templates (not a module)
│ ├── layout.mustache.html
│ └── home.mustache.html
├── public/ # static files, served directly
│ └── favicon.png
└── main.c # registers modules
Bundled modules (add the initializer to .modules to use): sqlite, postgres, mysql, redis, duckdb, htmx, datastar, tailwind, session_auth. See Module Reference for what each one provides.
Module Reference
htmx
Brings HTMX support to MACH apps: server-rendered partial updates, history, request indicators, all driven by HTML attributes on the elements that need them.
Partial: {{>htmx}}, the script tag for the HTMX runtime, served through MACH. Include in <head>.
Context flags:
is_htmx: true when the request has theHX-Requestheader. Pair with.if_context = "is_htmx"to send fragments to HTMX requests and full pages to direct loads.
Example. A SPA-feel app with no pipeline branching: hx-boost='true' on <body> makes every <a> and <form> inside use AJAX navigation, swapping body content instead of full page reloads. Boosted requests come through the normal pipelines.
render(.template =
"<html>"
"<head>{{>htmx}}</head>"
"<body hx-boost='true'>"
"<nav><a href='{{url:home}}'>Home</a></nav>"
"<main>...</main>"
"</body>"
"</html>")
For HTMX attributes (hx-boost, hx-target, hx-swap, etc.), see the HTMX docs.
datastar
Brings Datastar support: hypermedia-driven reactive frontend where the server pushes DOM updates and reactive signal state over SSE.
Partial: {{>datastar}}, the script tag for the Datastar runtime, served through MACH. Include in <head>.
Context flags:
is_ds: true when the request originates from the Datastar client. Pair with.if_context = "is_ds"to send Datastar SSE events back to Datastar requests and full pages to direct loads.
Steps:
ds_sse(...): combines SSE with Datastar-formatted events targeting specific elements. Without a channel the event goes to the requesting client; with one it broadcasts.
ds_sse fields:
.channel (pos): broadcast channel; supports {{interpolation}}.
ds_sse("todos/{{user_id}}", .target = "todos", .elements = {"todo"})
.target: DOM element id for the update.
ds_sse(.target = "todos", .elements = {"todo_row"})
.mode: fragment insertion mode for the rendered DOM fragment.
ds_sse(.target = "todos", .mode = mode_prepend, .elements = {"todo_row"})
.elements: a render_config for the DOM fragment (positional is the asset name, supports .template, .engine, etc.).
ds_sse(.target = "row", .elements = {"todo_row"})
.signals: JSON string used to update Datastar's reactive client state without touching the DOM.
ds_sse(.signals = "{\"count\": {{count}}}")
.js: JavaScript snippet evaluated on the client.
ds_sse(.js = "console.log('updated')")
Types: ds_mode enum with values mode_outer, mode_inner, mode_replace, mode_prepend, mode_append, mode_before, mode_after, mode_remove.
Example. Append a new todo row to the live list across all clients on the channel:
.post = {
validate({"title", .validation = validate_not_empty}),
query({.set_key = "new_todo", .db = "todos_db",
.query = "insert into todos(title) values({{title}}) returning id, title;"}),
ds_sse("todos",
.target = "#todo-list",
.mode = mode_append,
.elements = {.template = "{{#new_todo}}<li id='todo-{{id}}'>{{title}}</li>{{/new_todo}}"}),
redirect("todos")
}
For Datastar attributes, signals, and the wire-format SSE events that ds_sse produces, see the Datastar reference and specifically SSE Events.
tailwind
Brings Tailwind CSS to MACH apps.
Partial: {{>tailwind}}, the standard Tailwind CDN runtime, served through MACH. Include in <head>.
Example.
render(.template =
"<html>"
"<head>{{>tailwind}}</head>"
"<body class='bg-gray-50 text-gray-900 p-8'>"
"<h1 class='text-2xl font-bold'>Welcome</h1>"
"</body>"
"</html>")
For utility classes and configuration, see the Tailwind docs.
session_auth
Adds session-based authentication: cookie-backed sessions, login/logout/signup actions, a guard step that redirects unauthenticated users to the login page, and a step that loads the full user record into context.
Steps:
logged_in(): guard that redirects to theloginresource when there's no active session. When there is one, setsuser_idin context. Drop into a resource's shared.stepsslot to gate the whole resource.session(): takesuser_idfrom context and loads the full user record into context asuser, includingid,full_name,short_name. Run afterlogged_in()when verb pipelines need user details beyond just the id; skip it when onlyuser_idis needed.login(),logout(),signup(): available for custom auth flows where you want to handle the action yourself. Most apps don't need these;session_authprovides/login,/logout, and/signupresources internally.
The login page's template is whatever asset is registered under the name login in .context. Override it to use your own form.
Example. A protected dashboard with full user info available:
{"dashboard", "/dashboard", {logged_in(), session()},
.get = {
render(.template = "{{#user}}<h1>Welcome, {{full_name}}</h1>{{/user}}")
}
}
For a resource that only needs the user id, drop session() and use just logged_in():
{"my_todos", "/me/todos", {logged_in()},
.get = {
query({.set_key = "todos", .db = "todos_db",
.query = "select id, title from todos where user_id = {{user_id}};"}),
render("todos")
}
}
To customize the login page, register your own template under the name login in .context. The form posts to /login, where session_auth's internal handler validates and authenticates.
static/login.mustache.html
<html><body>
<h1>Sign in</h1>
<form method='post' action='{{url:login}}'>
{{csrf:input}}
<label>Username <input name='username' value='{{input:username}}' required></label>
{{#error:username}}<span>{{error_message:username}}</span>{{/error:username}}
<label>Password <input name='password' type='password' required></label>
{{#error:password}}<span>{{error_message:password}}</span>{{/error:password}}
<button>Sign in</button>
</form>
</body></html>
.context = {
{"login", (asset){
#embed "static/login.mustache.html"
}}
}
Schema for users and sessions is created automatically on first boot.
Database engines (sqlite, postgres, mysql, redis, duckdb)
Each engine module enables one <engine>_db constant for use in .databases.engine, and registering the module is required for any database that uses it. MACH wraps each engine's native driver, so connection strings are passed through verbatim and accept whatever the underlying driver accepts.
| Module | Engine constant | Docs |
|---|---|---|
sqlite |
sqlite_db |
SQLite |
postgres |
postgres_db |
PostgreSQL |
mysql |
mysql_db |
MySQL |
redis |
redis_db |
Redis |
duckdb |
duckdb_db |
DuckDB |
Connection strings support {{interpolation}} for multi-tenant setups (see Databases).
Example. Same shape regardless of engine; only .engine, .connect, and the registered module change:
.databases = {{
.engine = postgres_db,
.name = "blog_db",
.connect = "postgres://user:pass@localhost:5432/blog",
.migrations = { "CREATE TABLE posts (...);" }
}},
.modules = {postgres}
Static Files
Files in public/ at the project root are served directly. Use it for images, fonts, pre-built CSS/JS, and other assets that don't need to be embedded in the binary. Reference them with {{asset:filename}}, which resolves to a URL with a content checksum and immutable cache headers.
public/ directory: drop in static files; they are served at the root URL space.
public/
├── favicon.png
├── logo.png
└── styles.css
{{asset:filename}}: cache-busting helper for use inside templates.
<link rel="icon" href="{{asset:favicon.png}}">
<link rel="stylesheet" href="{{asset:styles.css}}">
<script src="{{asset:app.js}}"></script>
External Dependencies
MACH expects a containerized development environment: write standard C23 against the MACH APIs, no local toolchain required. Two ways to bring in third-party C libraries, plus two helpers for bridging foreign memory back to the arena.
/vendor directory: drop headers and libraries (.so, .a) here; the auto-compiler discovers, includes, and links them.
/vendor/
├── libsodium.h
└── libsodium.so
Custom Dockerfile: inherit from the MACH base image and apt-get install system dependencies; reference it from compose.yml.
FROM mach:latest
RUN apt-get update && apt-get install -y libsodium-dev
allocate(bytes): provides a buffer from the pipeline arena, reclaimed on request completion.
char *buf = allocate(256);
defer_free(ptr): schedules cleanup for pointers returned by external libraries (e.g. via malloc); runs when the arena is released.
char *out = third_party_alloc(256);
defer_free(out);
Architecture
How MACH compiles, executes, and protects an application at runtime.
Data-Oriented Pipelines
The mach() function runs once at boot. The returned config is processed into an execution graph with precompiled pipelines, queries, and templates. Each incoming request then executes its matching pipeline as a sequence of pre-warmed steps.
Multi-Reactor Architecture
MACH runs two types of reactors backed by a shared thread pool. The request/task/cpu ratio can be set in compose.yml.
- Request reactors handle HTTP traffic; each gets its own dedicated CPU core and event loop.
- Task reactors handle background work; each gets its own dedicated core, monitors the task database for pending and incomplete tasks, and processes cron schedules.
- Shared thread pool handles CPU-bound and blocking I/O work on the remaining cores.
When any reactor's pipeline executes an exec() step, the work is dispatched to the shared thread pool, which releases the reactor. When the call completes, the pipeline resumes on the original reactor. The task() step adds jobs to the task database, where they are picked up by task reactors. Tasks can call task() themselves to enqueue additional work.
Application code does not manage threads, mutexes, or locks. The architecture isolates request state to the pipeline's context.
Safe by Default
MACH prevents common C and web vulnerabilities at the framework level.
Memory Safety
Each reactor maintains a pool of arena allocators. When a request arrives, the pipeline is assigned an arena, and all allocations draw from it. When the pipeline completes, the arena is cleared and returned to the pool. Application code does not call malloc or free, which avoids leaks, double-frees, and use-after-free.
All framework data structures (tables, records, strings) enforce bounds checking. Out-of-bounds reads and missing context values return nullptr rather than faulting. Pipelines that exceed their memory limit (default 5MB, configurable in compose.yml) abort with a 500, mitigating OOM denial-of-service.
SQL Injection Prevention
Interpolations such as {{user_id}} inside query() or find() are bound as parameters in prepared statements, preventing SQL injection at the framework level.
XSS Prevention
The render() step auto-escapes context values in Mustache templates, so malicious input is rendered as text. Raw HTML requires explicit opt-in via Mustache's standard unescape syntax: {{{field}}} or {{&field}}.
String Interpolation
Any string (SQL queries, URLs, connection strings, templates) can reference values from the context with {{context_key}}. The same scopes described in Context apply everywhere interpolation is used.
Tooling
- Development Environment
- Introspection
- Testing
- Debugging
- Deployment
- Observability
- Project Management
- Built With
Development Environment
Built-in TUI editor with HMR, LSP support, integrated source control, and a topology-aware AI assistant. The AI uses the app_info command to inspect the full application topology (routes, pipelines, database schemas, event contracts, and module boundaries), so it reasons about the application's actual execution graph rather than just source text.
Introspection
app_info # view topology
app_info resources # list all resources
app_info pipelines # inspect pipelines
app_info events # view pub/sub map
app_info databases # inspect schemas
Testing
Built-in test runners for unit and end-to-end testing; no external framework setup required.
unit_tests # fast, criterion-based tests
e2e_tests # playwright-powered browser tests
Debugging
Built-in debugging with pipeline-aware commands. Halt on individual pipeline steps, step through execution, and inspect the full pipeline context including nested tables and records.
app_debug # interactive debugger in the TUI
Deployment
MACH deploys as a standard Docker container. It does not terminate TLS; production deployments place MACH behind a reverse proxy or load balancer (Nginx, Caddy, AWS ALB) to handle HTTPS.
app_build # outputs slim, optimized production Docker image
Observability
Each pipeline step emits OpenTelemetry spans. Logs, traces, errors, and auto-profiling are visualized on the telemetry server at port 4000. No manual instrumentation required.
Project Management
MACH ships with integrated project infrastructure: source control, issue tracking, wiki, forum, and a project website.
Built With
| C23 | Language standard |
| Docker | Development environment, production images, stack orchestration |
| libmicrohttpd / libuv | HTTP server, event loops, async I/O, file watching, shared thread pool |
| Mustach | Templating and string interpolation |
| Jansson | JSON parsing and generation |
| curl | HTTP client for fetch steps |
| Fossil | Source control, wiki, forum, issue tracker, project site |
| Fresh | TUI editor |
| clangd | Language server |
| LLDB | Debugger |
| Criterion | Unit testing |
| Playwright | End-to-end testing |
| SigNoz + OpenTelemetry | APM, traces, logs, errors, dashboards |
| Open Code | AI assistant with custom agent and skill files |
License
MACH is licensed under the LGPL.