MACH

Why MACH

MACH (Modern Asynchronous C Hypermedia) is a declarative framework for building asynchronous web applications in C23.

• No build configuration. Compilation, hot code reloading, and HMR are handled by the framework. No build scripts, package managers, or ORMs. SQL and HTML assets are discovered automatically.
• Memory, concurrency, and I/O managed by the framework. Application code does not call malloc/free or manage threads, mutexes, or locks. Queries run as prepared statements. Pipeline steps emit OpenTelemetry spans, logs, and errors automatically.
• Durable tasks and events. Both are persisted. After a crash, incomplete tasks resume at the step where they stopped and undelivered events replay on the next boot.
• Bundled modules. Datastar, HTMX, Tailwind, SQLite, Postgres, MySQL, Redis/Valkey, DuckDB, and auth. Multi-tenant database support is built in.

---

Table of Contents

• Quick Start
• Philosophy
• Guide
• Reference
• Architecture
• Tooling
• License

---

Quick Start

Everything runs in Docker. No other local dependencies.

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 editor, AI, LSP, and console.

#include <mach.h>

mach(){
  context("hello", "<h1>Hello, world!</h1>");
  resource("home", "/", .get = {mustache("hello")});
}

mach() runs once at boot and declares the application. context() registers a named template inline; resource() declares the home endpoint mapping / to a GET pipeline that renders that template. See the Guide for a step-by-step walkthrough.

---

Philosophy

An application is a data transformation: input arrives, gets transformed, leaves as output. MACH is a thin pipeline wrapper around that path.

All assets and toolimg are standard: raw SQL, JSON, Markdown, and HTML/CSS/JS via Mustache templates, business logic is plain C, lldb for debugging, Playwright and Criterion for testing, OpenTelemetry for observability, OpenCode for AI. MACH arranges these into pipelines: ordered lists of steps that turn a request into a response.

Everything is a String

The web is text: HTTP, HTML, JSON, SQL. The pipeline context stores and passes data as strings. There is no intermediate parsing or serialization layer. Strings are interpolated into SQL, templates, and URLs with {{context_key}}.

CLAD

Four principles:

• (C)omposable: small, independent steps chain into feature pipelines.
• (L)ocality of Behavior: behavior is apparent from reading the code. SQL, templates, and logic for a feature live together, not spread across model, view, and controller trees.
• (A)utonomous: modules are self-contained: own schemas, migrations, seeds, routes, UI, and logic. The compiler enforces boundaries.
• (D)omain Based: each module owns one slice of the app. A todos module defines everything related to todos and nothing else.

Influenced by:

• Data Oriented Design
• A Philosophy of Software Design
• CUPID
• Self-Contained Systems
• Locality of Behavior

---

Guide

Builds a todo app one concept at a time. See the Reference for full options on each step, helper, and field. MACH discovers assets automatically and seeds each into the context of the module that owns it, based on file location (see Assets).

• 1. Pages and Templates
• 2. Show Data
• 3. Accept Input
• 4. Nested Data
• 5. Tasks
• 6. Modules and Events
• 7. Calling APIs

1. Pages and Templates

Each resource(...) declares a named URL endpoint; each verb pipeline is a list of steps. mustache("home") renders the template asset home, which is the file home.mustache.html. Reference resources by name with {{url:...}}.

Both pages share a layout, so home doubles as the layout: it declares the nav and a {{$body}} block whose default is the welcome page. The todos page extends it with {{<home}}...{{/home}}, overriding that block. Any template that declares a {{$block}} can be a parent; there is no special layout type.

home.mustache.html

<html>
  <body>
    <nav><a href='{{url:home}}'>Home</a> · <a href='{{url:todos}}'>My Todos</a></nav>
    <main>{{$body}}<h1>Welcome</h1>{{/body}}</main>
  </body>
</html>

todos.mustache.html

{{<home}}
  {{$body}}
    <h1>My Todos</h1>
    <p>Nothing yet.</p>
  {{/body}}
{{/home}}

main.c

#include <mach.h>

mach(){
  resource("home", "/", .get = {mustache("home")});
  resource("todos", "/todos", .get = {mustache("todos")});
}

See Resource Pipelines and Templates.

2. Show Data

Bring in SQLite with #include <sqlite.h>, declare a database with sqlite_database(...), and read with sqlite_query(). SQL files are assets like templates: get_todos.sql becomes the asset get_todos.

Three new SQL files:

create_todos_table.sql

CREATE TABLE todos (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  title TEXT NOT NULL
);

seed_todos.sql

INSERT INTO todos(title) VALUES('Learn MACH');

get_todos.sql

select id, title from todos;

Render the rows MACH stores under todos_data:

todos.mustache.html

 {{<home}}
   {{$body}}
     <h1>My Todos</h1>
-    <p>Nothing yet.</p>
+    <ul>{{#todos_data}}<li>{{title}}</li>{{/todos_data}}</ul>
   {{/body}}
 {{/home}}

Wire up the module, database, and query:

main.c

 #include <mach.h>
+#include <sqlite.h>

 mach(){
+  sqlite_database(
+    "todos_db",
+    "file:todos.db?mode=rwc",
+    {"create_todos_table"},
+    {"seed_todos"}
+  );
+
   resource("home", "/", .get = {mustache("home")});
-  resource("todos", "/todos", .get = {mustache("todos")});
+
+  resource("todos", "/todos",
+    .get = {
+      sqlite_query({"todos_db", "get_todos", "todos_data"}),
+      mustache("todos")
+    }
+  );
 }

Query parameters: database name, SQL asset, context key for the result table (todos_data). The template walks the result with {{#todos_data}}...{{/todos_data}}. Migrations and seeds run on first connection. See Databases and query.

3. Accept Input

Add a .post verb that validates, inserts, and redirects (POST-redirect-GET). A resource-scoped .errors handler re-renders the form on validation failure.

create_todo.sql

insert into todos(title) values({{title}});

Add the form, repopulating the field and showing the error after a failed submit:

todos.mustache.html

 {{<home}}
   {{$body}}
     <h1>My Todos</h1>
     <ul>{{#todos_data}}<li>{{title}}</li>{{/todos_data}}</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}}
 {{/home}}

Add a .post verb and an .errors handler:

main.c

 #include <mach.h>
 #include <sqlite.h>

 mach(){
   sqlite_database(
     "todos_db",
     "file:todos.db?mode=rwc",
     {"create_todos_table"},
     {"seed_todos"}
   );

   resource("home", "/", .get = {mustache("home")});

   resource("todos", "/todos",
     .get = {
       sqlite_query({"todos_db", "get_todos", "todos_data"}),
       mustache("todos")
-    }
+    },
+    .post = {
+      input({"title", m_not_empty}),
+      sqlite_query({"todos_db", "create_todo"}),
+      redirect("todos")
+    },
+    .errors = {
+      {m_bad_request, {reroute("todos")}}
+    }
   );
 }

input() validates and promotes title to app scope; the {{title}} in create_todo.sql binds as a prepared-statement parameter. On failure, m_bad_request triggers the handler, which reroutes back into the GET pipeline in-process. The input: and error: scopes survive the reroute, so the form repopulates with {{input:title}} and shows {{error_message:title}}. See input, Error and Repair Pipelines, and redirect and reroute.

4. Nested Data

A /todos/:id page fetches a todo and its comments concurrently, then nests the comments inside the todo with join().

Three new SQL files and one new template:

create_comments_table.sql

CREATE TABLE comments (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  todo_id INTEGER NOT NULL REFERENCES todos(id),
  body TEXT NOT NULL
);

get_todo.sql

select id, title from todos where id = {{id}};

get_comments.sql

select id, todo_id, body from comments where todo_id = {{id}};

Enter {{#todo_data}} first; after the join, comments lives inside each todo record:

todo.mustache.html

{{<home}}
  {{$body}}
    {{#todo_data}}
      <h1>{{title}}</h1>
      <h2>Comments</h2>
      <ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>
    {{/todo_data}}
  {{/body}}
{{/home}}

Link each list item to its detail page. {{url:todo}} resolves to the todo resource's pattern (/todos/:id) and fills :id from the current row, so no argument is needed:

todos.mustache.html

 {{<home}}
   {{$body}}
     <h1>My Todos</h1>
-    <ul>{{#todos_data}}<li>{{title}}</li>{{/todos_data}}</ul>
+    <ul>{{#todos_data}}<li><a href='{{url:todo}}'>{{title}}</a></li>{{/todos_data}}</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}}
 {{/home}}

Register the migration and add a todo resource:

main.c

 #include <mach.h>
 #include <sqlite.h>

 mach(){
   sqlite_database(
     "todos_db",
     "file:todos.db?mode=rwc",
-    {"create_todos_table"},
+    {"create_todos_table", "create_comments_table"},
     {"seed_todos"}
   );

   resource("home", "/", .get = {mustache("home")});

   resource("todos", "/todos",
     .get = {
       sqlite_query({"todos_db", "get_todos", "todos_data"}),
       mustache("todos")
     },
     .post = {
       input({"title", m_not_empty}),
       sqlite_query({"todos_db", "create_todo"}),
       redirect("todos")
     },
     .errors = {
       {m_bad_request, {reroute("todos")}}
     }
   );
+
+  resource("todo", "/todos/:id",
+    .get = {
+      input({"id", m_integer}),
+      sqlite_query(
+        {"todos_db", "get_todo", "todo_data", .must_exist = true},
+        {"todos_db", "get_comments", "comments"}
+      ),
+      join("todo_data", "id", "comments", "todo_id"),
+      mustache("todo")
+    }
+  );
 }

Both queries in one sqlite_query() call run concurrently. join() lifts comments inside each todo_data record, so the template reaches {{#comments}} from within {{#todo_data}}. .must_exist = true returns 404 when the id matches nothing. See join and query.

5. Tasks

A task is a named pipeline that runs off the request path on a task reactor. Define it once with optional .cron; enqueue on-demand runs with run("name").

Two new SQL files:

create_daily_stats_table.sql

CREATE TABLE daily_stats (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  todo_count INTEGER NOT NULL
);

record_daily_stats.sql

insert into daily_stats(todo_count) select count(*) from todos;

Register the migration, define the task, enqueue it from the POST:

main.c

 #include <mach.h>
 #include <sqlite.h>
+#include <task.h>

 mach(){
   sqlite_database(
     "todos_db",
     "file:todos.db?mode=rwc",
-    {"create_todos_table", "create_comments_table"},
+    {"create_todos_table", "create_comments_table", "create_daily_stats_table"},
     {"seed_todos"}
   );

+  task("record_daily_stats", {
+    sqlite_query({"todos_db", "record_daily_stats"})
+  }, .cron = "0 0 * * *");
+
   resource("home", "/", .get = {mustache("home")});

   resource("todos", "/todos",
     .get = {
       sqlite_query({"todos_db", "get_todos", "todos_data"}),
       mustache("todos")
     },
     .post = {
       input({"title", m_not_empty}),
       sqlite_query({"todos_db", "create_todo"}),
+      run("record_daily_stats"),
       redirect("todos")
     },
     .errors = {
       {m_bad_request, {reroute("todos")}}
     }
   );

   resource("todo", "/todos/:id",
     .get = {
       input({"id", m_integer}),
       sqlite_query(
         {"todos_db", "get_todo", "todo_data", .must_exist = true},
         {"todos_db", "get_comments", "comments"}
       ),
       join("todo_data", "id", "comments", "todo_id"),
       mustache("todo")
     }
   );
 }

.cron and run("record_daily_stats") both run the task on a task reactor, off the request reactors, so the POST returns immediately. Tasks are durable: a crash mid-task resumes on the next boot. To hand values to a task, list them under .accepts. See Task Pipelines.

6. Modules and Events

Split features into modules that talk through pub/sub events. A module is a folder with a matching .c file (todos/todos.c) declaring module(todos){ ... }, which registers the module's resources, databases, tasks, and subscribers. Assets in the folder belong to the module. main.c composes modules by #includeing each .c file; the include is all that is needed.

This step moves todos into its own module and adds an activity module that records an entry whenever a todo is created. Move the todos assets into todos/, add the new activity/ folder, leave home (the shared layout) at the root:

.
├── todos/
│   ├── todos.c
│   ├── todos.mustache.html
│   ├── todo.mustache.html
│   ├── create_todos_table.sql
│   ├── seed_todos.sql
│   ├── get_todos.sql
│   ├── get_todo.sql
│   ├── get_comments.sql
│   └── create_todo.sql
├── activity/
│   ├── activity.c
│   ├── activity.mustache.html
│   ├── create_activity_table.sql
│   ├── get_activities.sql
│   └── insert_activity.sql
├── home.mustache.html
└── main.c

main.c collapses to a thin composer:

main.c

 #include <mach.h>
-#include <sqlite.h>
-#include <task.h>
+#include "todos/todos.c"
+#include "activity/activity.c"

 mach(){
-  sqlite_database(
-    "todos_db",
-    "file:todos.db?mode=rwc",
-    {"create_todos_table", "create_comments_table", "create_daily_stats_table"},
-    {"seed_todos"}
-  );
-
-  task("record_daily_stats", {
-    sqlite_query({"todos_db", "record_daily_stats"})
-  }, .cron = "0 0 * * *");
-
   resource("home", "/", .get = {mustache("home")});
-
-  resource("todos", "/todos",
-    .get = {
-      sqlite_query({"todos_db", "get_todos", "todos_data"}),
-      mustache("todos")
-    },
-    .post = {
-      input({"title", m_not_empty}),
-      sqlite_query({"todos_db", "create_todo"}),
-      run("record_daily_stats"),
-      redirect("todos")
-    },
-    .errors = {
-      {m_bad_request, {reroute("todos")}}
-    }
-  );
-
-  resource("todo", "/todos/:id",
-    .get = {
-      input({"id", m_integer}),
-      sqlite_query(
-        {"todos_db", "get_todo", "todo_data", .must_exist = true},
-        {"todos_db", "get_comments", "comments"}
-      ),
-      join("todo_data", "id", "comments", "todo_id"),
-      mustache("todo")
-    }
-  );
 }

Add an Activity link to the shared nav:

home.mustache.html

 <html>
   <body>
-    <nav><a href='{{url:home}}'>Home</a> · <a href='{{url:todos}}'>My Todos</a></nav>
+    <nav><a href='{{url:home}}'>Home</a> · <a href='{{url:todos}}'>My Todos</a> · <a href='{{url:activity}}'>Activity</a></nav>
     <main>{{$body}}<h1>Welcome</h1>{{/body}}</main>
   </body>
 </html>

The todos logic moves into the module unchanged, gaining a publish() and an emit() step. Both todo resources come along:

todos/todos.c

#include <mach.h>
#include <sqlite.h>
#include <pubsub.h>
#include <task.h>

module(todos){
  sqlite_database(
    "todos_db",
    "file:todos.db?mode=rwc",
    {"create_todos_table", "create_comments_table", "create_daily_stats_table"},
    {"seed_todos"}
  );

  publish("todo_created", .with = {"title"});

  task("record_daily_stats", {
    sqlite_query({"todos_db", "record_daily_stats"})
  }, .cron = "0 0 * * *");

  resource("todos", "/todos",
    .get = {
      sqlite_query({"todos_db", "get_todos", "todos_data"}),
      mustache("todos")
    },
    .post = {
      input({"title", m_not_empty}),
      sqlite_query({"todos_db", "create_todo"}),
      run("record_daily_stats"),
      emit("todo_created"),
      redirect("todos")
    },
    .errors = {
      {m_bad_request, {reroute("todos")}}
    }
  );

  resource("todo", "/todos/:id",
    .get = {
      input({"id", m_integer}),
      sqlite_query(
        {"todos_db", "get_todo", "todo_data", .must_exist = true},
        {"todos_db", "get_comments", "comments"}
      ),
      join("todo_data", "id", "comments", "todo_id"),
      mustache("todo")
    }
  );
}

The activity module owns its own table, query, template, and subscriber. Nothing in it references the todos module:

activity/create_activity_table.sql

CREATE TABLE activities (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  kind TEXT NOT NULL,
  ref TEXT NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

activity/insert_activity.sql

insert into activities(kind, ref) values('created', {{title}});

activity/get_activities.sql

select kind, ref, created_at from activities order by created_at desc;

activity/activity.mustache.html

{{<home}}
  {{$body}}
    <h1>Activity</h1>
    <ul>{{#activities}}<li>{{kind}}: {{ref}} ({{created_at}})</li>{{/activities}}</ul>
  {{/body}}
{{/home}}

activity/activity.c

#include <mach.h>
#include <sqlite.h>
#include <pubsub.h>

module(activity){
  sqlite_database(
    "activity_db",
    "file:activity.db?mode=rwc",
    {"create_activity_table"}
  );

  subscribe("todo_created", {
    sqlite_query({"activity_db", "insert_activity"})
  });

  resource("activity", "/activity",
    .get = {
      sqlite_query({"activity_db", "get_activities", "activities"}),
      mustache("activity")
    }
  );
}

When the POST calls emit("todo_created"), MACH propagates the keys named in publish(...).with (title) to every subscriber. The activity module writes its row with no direct link to the publisher. Events are durable: undelivered ones replay after a crash. Adding a third subscriber is a new file with its own subscribe(...); the publisher does not change. See Modules and Composition and Event Pipelines.

7. Calling APIs

fetch() calls external HTTP services like a query calls a database. JSON parses into context tables; multiple items in one fetch() run concurrently.

Show the responses on the home page:

home.mustache.html

 <html>
   <body>
     <nav><a href='{{url:home}}'>Home</a> · <a href='{{url:todos}}'>My Todos</a> · <a href='{{url:activity}}'>Activity</a></nav>
-    <main>{{$body}}<h1>Welcome</h1>{{/body}}</main>
+    <main>{{$body}}
+      <h1>Welcome</h1>
+      {{#weather}}<p>{{city}}: {{precision:temp_c:0}}°C, {{conditions}}</p>{{/weather}}
+      {{#quote}}<blockquote>{{content}}, {{author}}</blockquote>{{/quote}}
+    {{/body}}</main>
   </body>
 </html>

Fetch both services concurrently before rendering:

main.c

 #include <mach.h>
 #include "todos/todos.c"
 #include "activity/activity.c"

 mach(){
-  resource("home", "/", .get = {mustache("home")});
+  resource("home", "/",
+    .get = {
+      fetch(
+        {"https://api.quotes.dev/random", "quote"},
+        {"https://api.weather.dev/now", "weather"}
+      ),
+      mustache("home")
+    }
+  );
 }

Both requests run concurrently under one fetch() call. The JSON parses into context tables the template walks with {{#quote}} and {{#weather}}. fetch() also supports other verbs, headers, request bodies, and interpolated URLs. See fetch.

---

Reference

• Context
• Templates
• Assets
• Databases
• Resource Pipelines
• Pipeline Steps
• Imperative API
• Conditionals
• Iteration
• Error and Repair Pipelines
• Event Pipelines
• Task Pipelines
• Modules and Composition
• Module Reference
• Static Files
• External Dependencies

Context

Pipelines read from and write to a shared, scoped key-value store that lives for one request. Every step draws inputs from context and writes outputs back.

Three scopes: input:xxx for raw request parameters, error:xxx for validation/error data, and unprefixed names for app scope (query results, validated inputs, computed values). input() promotes values from input: to app scope.

Templates

MACH uses Mustache and MDM (Mustache + Markdown) templates. The full Mustache base spec is supported except dot notation: {{a.b}} does not work; use {{#a}}{{b}}{{/a}}.

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 asset name, rendered against the current scope.
• Layout inheritance: {{<parent}}{{$block}}override{{/block}}{{/parent}} renders parent with each {{$block}}default{{/block}} block replaced by the override. Any asset declaring blocks can be a parent.

Built-in helpers use {{helper:args}} syntax. Arguments are colon-separated, in order; each can be a literal or a context key.

{{precision:field:N}}: format a numeric value with N decimal places.

<p>Total: ${{precision:total:2}}</p>

{{input:field}}: raw, unvalidated request parameter from the input scope. Used to repopulate form fields after a validation error.

<input name='title' value='{{input:title}}'>

{{error:field}}: truthy when field has an error. Used as a Mustache section to conditionally render markup.

{{#error:title}}<span class='error'>invalid</span>{{/error:title}}

{{error_message:field}}: human-readable message for a field error, from input()'s message or from error_set().

<span>{{error_message:title}}</span>

{{error_code:field}}: HTTP status code associated with a field error (e.g. 400, 404).

<p>Code: {{error_code:title}}</p>

{{url:name}}: resolve a resource name to its URL. :params in the URL pattern are read from the current scope by name.

<a href='{{url:todos}}'>All</a> <!-- /todos -->
{{#todos_data}}<a href='{{url:todo}}'>{{title}}</a>{{/todos_data}} <!-- /todos/:id, filled per row -->
{{#todo}}<a href='{{url:todo}}'>{{title}}</a>{{/todo}} <!-- /todos/:id, from a single record -->

{{asset:filename}}: resolve a file in public/ to a cache-busted URL (content checksum + immutable cache headers). See Static Files.

<link rel='stylesheet' href='{{asset:styles.css}}'>

{{csrf:token}}: emit a CSRF token for URL query strings. Generates a random hash, sets it on an httponly/secure/samesite cookie, outputs the same value inline.

<a href='{{url:logout}}?csrf={{csrf:token}}'>Log out</a>

{{csrf:input}}: emit a hidden <input> carrying a CSRF token, for <form> use. Same cookie behavior as {{csrf:token}}.

<form>{{csrf:input}}<input name='title'><button>Add</button></form>

---

Assets

Every non-.c file is an asset. Assets are embedded into the binary at compile time and loaded into context at startup under their name, in the module they belong to, as if context(name, contents) had been called there. Common types are Mustache templates (*.mustache.html), Markdown (*.md), and SQL (*.sql); the rule is general.

An asset's name is the filename's basename (the part before the first dot). get_todos.sql seeds get_todos, todos.mustache.html seeds todos, home.md seeds home. Steps read these like any other context value: mustache("todos"), sqlite_query({"todos_db", "get_todos", "todos_data"}), and .migrations/.seeds entries ({"create_todos_table"}).

mustache(), mdm(), and the engine *_query() steps read a string from context by key and interpret it as a template or SQL. The step interprets whatever is under the key when it runs.

context(name, value) does the same seeding from a string instead of a file. Useful for content too small to warrant its own file:

context("hello", "<h1>Hello, world!</h1>"); // then mustache("hello")
context("ping", "select 1");                // then sqlite_query({"db", "ping"})

An asset is seeded into the module whose folder it sits in. A folder is a module when it contains a matching <folder>.c file (so todos/ is a module when todos/todos.c exists); folders without one are organizational and pass their files up to the enclosing module. The project root is the main module. Walking up from a file's location, it seeds in the nearest module folder:

.
├── main.c # the "main" module (root)
├── home.mustache.html # → main
├── partials/
│   └── footer.mustache.html # → main (partials/ has no partials.c)
└── todos/
    ├── todos.c # the "todos" module
    ├── todos.mustache.html # → todos
    └── detail/
        └── todo.mustache.html # → todos (detail/ has no detail.c)

Once seeded, the key resolves like any other context value across modules; see Context.

Databases

Each database engine is a module: #include its header (e.g. #include <sqlite.h>) to activate it, then register a database with <engine>_database(...). Migrations and seeds are forward-only and index-based: they run in array order, each applied once, with new ones appended to the end. Both are tracked in a mach_meta table.

Multi-tenant databases use {{interpolation}} in .connect. Connections are pooled with LRU eviction.

.name: identifier referenced by the first value of query() steps.

.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 entries, applied once each in order. Each entry is a context key holding the SQL.

.migrations = {"create_todos_table", "create_comments_table"}

.seeds: array of SQL seed entries, applied once each in order. Each entry is a context key holding the SQL.

.seeds = {"seed_todos"}

Combined:

#include <sqlite.h>

sqlite_database(
  "blog_db",
  "file:{{user_id}}_blog.db?mode=rwc",
  {"create_blogs_table", "create_comments_table"},
  {"seed_blogs"}
);

Engine include / query / register: #include <sqlite.h> + sqlite_query() + sqlite_database(), and likewise postgres_*, mysql_*, redis_*, duckdb_*.

Resource Pipelines

MACH is resource-based, not route-based. Each resource(...) defines a named URL endpoint with HTTP verb pipelines. {{url:name}}, redirect(), and reroute() all take only the resource name; :params are read from the current scope by matching key names. Path specificity is automatic: exact matches (/todos/active) take priority over parameterized matches (/todos/:id) regardless of definition order.

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.

Resource name (by order): identifier used by {{url:name}}, redirect(), and reroute().

resource("todos", "/todos", .get = { ... });

URL pattern (by order): URL pattern. Supports :params.

resource("todo", "/todos/:id", .get = { ... });

.all: shared steps that run before every verb pipeline on the resource.

resource("todo", "/todos/:id",
  .all = { input({"id", m_integer, "must be a number"}) },
  .get = { ... },
  .delete = { ... }
);

.mime: default response content type. Values: m_html, m_txt, m_sse, m_json, m_js (default m_html).

resource("feed", "/feed.json", .mime = m_json, .get = { ... });

.get .post .put .patch .delete: verb pipelines: ordered arrays of steps that transform a request into a response.

resource("todos", "/todos",
  .get = { sqlite_query({"db", "get_todos", "todos_data"}), mustache("todos") },
  .post = { input({"title", m_not_empty}), redirect("todos") }
);

.sse: persistent SSE channel. The first value is the channel name (supports {{interpolation}}); any remaining steps run on connect.

resource("todos", "/todos",
  .sse = {"todos:{{user_id}}",
    sqlite_query({"db", "get_todos", "todos_data"}),
    sse(.event = "initial", .data = {"{{todos_data}}"})
  }
);

.errors / .repairs: resource-scoped error and repair pipelines. See Error and Repair Pipelines.

resource("todos", "/todos",
  .post = { ... },
  .errors = {{m_bad_request, {mustache("form")}}}
);

Combined:

resource("todo", "/todos/:id",
  .all = { input({"id", m_positive, "must be a number"}) },
  .get = { sqlite_query({"todos_db", "get_todo", "todo", .must_exist = true}),
              mustache("todo") },
  .patch = { input({"title", m_not_empty, "required"}),
              sqlite_query({"todos_db", "update_todo"}),
              redirect("todo") },
  .delete = { sqlite_query({"todos_db", "delete_todo"}),
              redirect("todos") },
  .sse = {"todo:{{id}}", sse(.event = "ready") },
  .errors = {{m_not_found, {mustache("404")}}}
);

Pipeline Steps

Steps are the units of work in a pipeline. Each receives the current context, acts on it, passes control to the next. All steps accept .if_context/.unless_context for conditional execution, and .table_key for concurrent fan-out across rows of a context table (see Iteration).

Concurrency comes from multiple items inside one step, not multiple steps in sequence. sqlite_query({...}, {...}) runs both queries concurrently; two back-to-back sqlite_query({...}) steps run serially. Same for fetch() and .table_key iteration.

• input
• query
• join
• fetch
• exec and worker
• emit
• run
• sse
• render
• headers and cookies
• redirect and reroute
• nest

input

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 m_zipcode "^\\d{5}$".

.param_key (by order): name of the parameter to validate.

input({"title", "^\\S+$", "required"})

.matches (by order): regex pattern, or a built-in validator macro.

input({"email", m_email, "bad email"})

.message (by order): human-readable error shown via {{error_message:name}}.

input({"age", m_integer, "must be a number"})

.optional: skip validation when the parameter is absent.

input({"filter", "^(active|done)$", .optional = true})

.fallback: default value injected when the parameter is absent.

input({"page", m_integer, .fallback = "1"})

Combined:

input(
  {"email", m_email, "must be a valid email"},
  {"title", m_not_empty, "cannot be empty"},
  {"page", m_integer, "must be a number", .fallback = "1"},
  {"filter", "^(active|done)$", "must be 'active' or 'done'", .optional = true},
  {"username", m_username, "must be alphanumeric"}
)

For checks beyond regex (uniqueness, cross-field rules, lookups), pair input() with a query and exec():

input({"username", m_username, "must be alphanumeric"}),
sqlite_query({"users_db", "find_username", "existing"}),
exec(^(){
  auto rows = get("existing");
  if (rows && table_count(rows) > 0)
    error_set("username", (error){m_bad_request, "already taken"});
})

Built-in validators:

• Strings: m_not_empty, m_alpha, m_alphanumeric, m_slug, m_no_html
• Numbers: m_integer, m_positive, m_float, m_percentage
• Identity: m_email, m_uuid, m_username
• Dates & times: m_date, m_time, m_datetime
• Web: m_url, m_ipv4, m_hex_color
• Codes: m_zipcode_us, m_phone_e164, m_cron
• Security: m_token, m_base64
• Boolean: m_boolean, m_yes_no, m_on_off

query

Each engine provides its own query step: sqlite_query(), postgres_query(), mysql_query(), redis_query(), duckdb_query(). All share the same query_config shape. By order: first value is the database .name, second is the context key holding the SQL, third is the .set_key for the result table (even single-row results are tables). Multiple items in one step run concurrently. Queries use prepared statements; interpolated {{values}} are bound, not spliced. For transactions, put BEGIN/COMMIT/ROLLBACK in the SQL.

.db (by order): database name, matching the name a <engine>_database(...) was registered with.

sqlite_query({"todos_db", "get_todos", "todos_data"})

.query (by order): context key holding the SQL to run.

sqlite_query({"todos_db", "get_todos", "todos_data"})

.set_key (by order): context key for the result table. Optional; omit when the result isn't needed (e.g. an insert without RETURNING).

sqlite_query({"todos_db", "create_todo"}) // no result captured
sqlite_query({"todos_db", "get_todos", "todos_data"}) // result under "todos_data"

.must_exist: when true, raise 404 Not Found if the query affects/returns zero rows. Default false.

sqlite_query({"todos_db", "get_todo", "todo", .must_exist = true})

.if_context / .unless_context (per item): conditionally include or skip individual queries while running the others concurrently.

sqlite_query(
  {"db", "get_todos", "todos_data"},
  {"db", "get_urgent", "urgent", .if_context = "show_urgent"}
)

Combined:

sqlite_query(
  {"todos_db", "get_todos", "todos_data"},
  {"todos_db", "get_todo", "todo", .must_exist = true},
  {"todos_db", "get_urgent", "urgent", .if_context = "show_urgent"}
)

join

Nests records from one context table into each matching record of another, like a SQL JOIN in memory. Useful when records come from separate databases or queries. After the step, each outer record gains a new field holding its matched inner records.

.parent_key: outer table whose records receive nested children.

.parent_key = "projects"

.field_key: field on the outer table to match against.

.field_key = "id"

.child_key: inner table whose records get nested.

.child_key = "todos"

.child_field_key: field on the inner table that points at the outer.

.child_field_key = "project_id"

.join_field_key: new field on outer records holding the matched inner records. (defaults to .child_key)

.join_field_key = "todos"

Combined:

join("projects", "id", "todos", "project_id")

Full context example. Concurrent query → join() → mustache(): fetch parent and children from separate queries, render as one nested structure. Blog + comments, single database:

blog.mustache.html

<article>
  {{#blog}}
    <h1>{{title}}</h1>
    <div>{{content}}</div>
    <h2>Comments</h2>
    <ul>{{#comments}}<li>{{body}}</li>{{/comments}}</ul>
  {{/blog}}
</article>

resource("blog", "/blogs/:id",
  .get = {
    input({"id", m_integer}),

    // Fetch both concurrently: one query() call, two items
    sqlite_query(
      {"blog_db", "get_blog", "blog"},
      {"blog_db", "get_comments", "comments"}
    ),

    // Nest each comment into its matching blog record
    join("blog", "id", "comments", "blog_id"),

    // Enter {{#blog}} first; after join(), comments lives INSIDE each blog record
    mustache("blog")
  }
);

Context shape 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 parses into tables and records (nested tables for nested JSON); plain-text responses are stored as strings. Like query(), multiple items in one step run concurrently.

.url (by order): request URL; supports {{interpolation}}.

fetch({"https://api.weather.dev/forecast?city={{city}}", "w"})

.set_key: context key for the response.

fetch({"https://api.weather.dev/now", "weather"})

.method: HTTP method. Defaults to m_get. Values: m_get, m_post, m_put, m_patch, m_delete, m_sse_method.

fetch({"https://api.dev/charge", "r", m_post})

.headers: array of name/value pairs.

fetch({"https://api.dev/me", "r", .headers = {{"Authorization", "Bearer {{token}}"}}})

.json: context key serialized as the JSON request body.

fetch({"https://api.dev/charge", "receipt", m_post, "order"})

.text: context key sent as the plain-text request body.

fetch({"https://api.dev/log", "r", m_post, .text = "raw_body"})

.if_context / .unless_context (per item): conditionally include or skip individual requests while running others concurrently.

fetch(
  {"https://api.weather.dev/now", "weather"},
  {"https://api.quotes.dev/random", "quote", .if_context = "show_quote"}
)

Combined, single request:

fetch({"https://api.payments.dev/charge",
  "receipt",
  m_post,
  "order",
  {
    {"Authorization", "Bearer {{api_key}}"},
    {"Idempotency-Key", "{{order_id}}"}
  }
})

Combined, concurrent fan-out:

fetch(
  {"https://api.weather.dev/now?city={{city}}", "weather"},
  {"https://api.news.dev/headlines?topic={{topic}}", "news"},
  {"https://api.quotes.dev/random", "quote"}
)

exec and worker

exec() calls a C function or block with access to context via the Imperative API. It is where business logic and data shaping lives: enriching query results, aggregating, transforming data between steps, setting flags for conditional downstream steps. Call error_set() to trigger an error/repair pipeline.

worker() takes the same configuration as exec() but is for blocking or CPU-bound work: external C libraries, blocking I/O, heavy computation. The work is dispatched to the shared thread pool, releasing the reactor; the pipeline resumes on the original reactor when the call returns. Use worker() when the body would stall a request reactor.

Block (by order): 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 const t = get("challengers");
  auto const p0 = table_get(t, 0);
  auto const p1 = table_get(t, 1);
  record_set(p0, "opponent_id", record_get(p1, "id"));
  record_set(p1, "opponent_id", record_get(p0, "id"));
})

.call: reference to a named C function, for logic reuse across pipelines.

exec(.call = assign_opponents)

Inside blocks and .call 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 subscribe() pipelines, with no direct dependency on the emitter. See Event Pipelines.

Event name (by order): name of the event to publish.

emit("todo_created")

run

Adds a named job to the task database; the calling pipeline continues immediately. Task reactors pick up queued jobs and execute their pipelines. The task must be defined elsewhere with task(name, { ... }). See Task Pipelines.

Task name (by order): name of a defined task.

run("record_daily_stats")

sse

Pushes a Server-Sent Event. With .channel, the event broadcasts to all clients on that channel. Without it, the event returns to the requesting client. See Resource Pipelines.

.channel (by order): channel to broadcast on; supports {{interpolation}}.

sse("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("todos:{{user_id}}",
  .event = "todo_updated",
  .data = {"id: {{todo_id}}", "title: {{title}}"},
  .comment = "broadcast at {{timestamp}}"
)

render

Outputs a template using the current context. mustache() renders Mustache; mdm() renders Markdown-with-Mustache; json() renders JSON. All take the same render_config.

.context_key (by order): key of the context value to render. The value is the template string itself.

mustache("todos")

.status: HTTP response status (default m_ok). Values: m_ok (200), m_created (201), m_redirect (302), m_bad_request (400), m_not_authorized (401), m_not_found (404), m_error (500).

mustache("not_found", .status = m_not_found)

.mime: override the response content type. Values: m_html, m_txt, m_sse, m_json, m_js.

mustache("plain", .mime = m_txt)

JSON:

json("todos")

Markdown-with-Mustache:

context("welcome", "# Welcome, {{user_name}}");
mdm("welcome")

headers and cookies

Set HTTP response headers and cookies declaratively. Both accept an array of name/value pairs; values support {{interpolation}}.

Pairs (by order): 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 and 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 only the target resource name. :params in the target's URL pattern are read from the current context by matching key names.

Resource name (by order): target resource name. Required :params are read from context by name.

redirect("todos") // 302 to /todos
redirect("todo") // 302 to /todos/{{id}}, id read from context
redirect("org_todo") // 302 to /orgs/{{org}}/todos/{{id}}, org and id read from context
reroute("todo") // run that pipeline in-process, id read from context

nest

Groups multiple steps into a single composite step. Useful when applying one .if_context/.unless_context to several steps without repeating it.

.steps (by order): array of steps that run as a unit.

nest({sqlite_query({...}), emit("urgent_todo"), mustache("urgent")})

.if_context / .unless_context: condition applied to the whole group.

nest({sqlite_query({...}), emit("urgent_todo"), mustache("urgent")},
  .if_context = "is_urgent")

---

Imperative API

Functions called from exec()/worker() blocks and .call functions to read and write context, allocate memory, raise errors, and manipulate tables and records.

• context
• memory
• errors
• tables
• 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 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.

auto 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.

auto buf = allocate(256);

defer_free(ptr): schedules free() for a pointer returned by an external library. Runs when the arena is released.

auto out = third_party_alloc(256);
defer_free(out);

Combined:

worker(^(){
  auto url = allocate(512);
  build_signed_url(url, 512, get("path"));
  set("signed_url", url);

  auto raw = third_party_render_md(get("markdown"));
  defer_free(raw);
  set("html", raw);
})

errors

Raise field-scoped errors from exec() to trigger error/repair pipelines. 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){ m_bad_request, "token has expired" });

error_get(name): returns the error previously set on name.

auto e = error_get("token");

error_has(name): returns true when name has an error.

if (error_has("token")) { ... }

Combined:

exec(^(){
  auto token = get("token");
  if (!token || strlen(token) < 16) {
    error_set("token", (error){
      m_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.

auto t = table_new();

table_count(t): number of records in t.

auto n = table_count(get("todos"));

table_get(t, i): record at index i, or nullptr if out of range.

auto 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(^(){
  auto source = get("raw_users");
  auto active = table_new();
  for (int i = 0; i < table_count(source); i++) {
    auto u = table_get(source, i);
    auto 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; see Everything is a String.

record_new(): returns an empty record in the pipeline arena.

auto r = record_new();

record_get(r, name): string value of name, or nullptr if absent.

auto 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(^(){
  auto todos = get("todos");
  for (int i = 0; i < table_count(todos); i++) {
    auto t = table_get(todos, i);
    auto 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, naming a context variable. They work for any context value: validated inputs, query results, framework flags like is_htmx, or flags set from exec().

.if_context: context key. Step runs only when the value is present.

mustache("fragment", .if_context = "is_htmx")

.unless_context: context key. Step runs only when the value is absent.

mustache("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),
mustache("urgent_confirmation", .if_context = "is_urgent"),
mustache("standard_confirmation", .unless_context = "is_urgent")

Iteration

.table_key names a context table to iterate over. The step runs once per row with that row's fields in scope; all rows run concurrently, like multiple items in query() or fetch(). With a .set_key, results are collected into a table aligned with the input, one entry per row.

.table_key: name of a context table to iterate over.

// One request per row in `users`, all concurrent.
// Responses collected into `profiles`, aligned with `users`.
fetch({"https://api.users.dev/{{id}}", "profiles", .table_key = "users"})

Use .table_key for per-row work that doesn't fit a single query or request (e.g. external APIs without bulk endpoints).

Error and Repair Pipelines

When a step fails, execution halts and MACH looks for a handler matching the error code. It checks the resource's own .errors/.repairs first, then the error()/repair() handlers in that resource's module, and uses the first match. A resource handler overrides the module's for the same code.

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. Repairs resolve first; if no matching repair is found, resolution falls through to errors. Unhandled errors fall through to MACH's internal handler, which looks for a context template named after the error code, otherwise 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 input() failures and error_set() calls: {{error:name}}, {{error_code:name}}, {{error_message:name}}. The raw input value remains in input:name for re-rendering forms.

Resource-scoped (.errors / .repairs fields):

resource("todos", "/todos",
  .post = { ... },
  .errors = {
    {m_not_found, {mustache("404")}},
    {m_bad_request, {mustache("form")}}
  },
  .repairs = {
    {m_not_authorized, {exec(.call = refresh_session_token)}}
  }
);

Module-scoped (error() / repair() calls):

module(todos){
  error(m_error, {mustache("5xx")});
  error(m_not_found, {mustache("404")});
  repair(m_not_authorized, {exec(.call = refresh_session_token)});
  // ... resources ...
}

Built-in error codes: m_bad_request (400), m_not_authorized (401), m_not_found (404), m_error (500). Any integer works; the m_* 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 a subscribe(...) call; the publisher does not change. Activate with #include <pubsub.h> in any module that publishes or subscribes.

Events are durable. When a publisher is declared, MACH creates a mach_events database to track delivery. If the process crashes, undelivered events replay on the next boot.

publish(event, .with = {...}): declares an outbound event contract. First value is the event name; .with lists context keys to pass along.

publish("todo_created", .with = {"user_id", "title"});

subscribe(event, { steps }): registers a subscriber pipeline keyed by event name.

subscribe("todo_created", {
  sqlite_query({"activity_db", "insert_activity"})
});

emit(event): a pipeline step that fires the event (see emit).

emit("todo_created")

.errors / .repairs (per subscriber): each subscribe(...) can declare its own handlers, resolved the same way as resource pipelines (the subscriber's own handlers, then its module's). See Error and Repair Pipelines.

subscribe("todo_created", {
  sqlite_query({"activity_db", "insert_activity"})
}, .errors = {{m_error, {exec(.call = log_subscriber_failure)}}});

Combined:

// todos/todos.c: publisher
module(todos){
  publish("todo_created", .with = {"user_id", "title"});
  publish("todo_deleted", .with = {"user_id", "todo_id"});

  resource("todos", "/todos",
    .post = {
      input({"title", m_not_empty}),
      sqlite_query({"todos_db", "insert_todo"}),
      emit("todo_created"),
      redirect("todos")
    }
  );
}

// activity/activity.c: subscriber
module(activity){
  subscribe("todo_created", {
    sqlite_query({"activity_db", "insert_created_activity"})
  });
  subscribe("todo_deleted", {
    sqlite_query({"activity_db", "insert_deleted_activity"})
  });
}

Task Pipelines

Tasks are named pipelines that run asynchronously on task reactors. Fire-and-forget: the calling pipeline continues immediately. Defined at module or root scope. Triggered on demand with run("name") or on a schedule via .cron. Tasks can enqueue more tasks.

Registered with task(name, { pipeline }, ...): name, pipeline body, optional .cron/.accepts. Registration and enqueuing are separate: task(...) defines, run("name") (enqueue step) enqueues.

Tasks are durable: MACH creates a mach_tasks database and checkpoints context after each step. A crash mid-task resumes at the step where it stopped on the next boot.

Task name (by order): task identifier, enqueued via run("name").

task("recount", {
  sqlite_query({"db", "recount_todos"})
});

Pipeline (by order): the task's pipeline body, a brace block.

task("name", { sqlite_query({...}), emit("done"), run("followup") });

.accepts: context keys to pull from the caller into the task.

task("recount_todos", {
  sqlite_query({"db", "recount"})
}, .accepts = {"user_id"});

.cron: standard cron schedule for recurring tasks (no caller required).

task("daily_digest", {
  sqlite_query({"db", "digest"})
}, .cron = "0 8 * * *");

.errors / .repairs (per task): each task can declare its own handlers, resolved the same way as resource pipelines (the task's own handlers, then its module's). See Error and Repair Pipelines.

task("send_invoice", {
  fetch({"https://api.billing.dev/invoices/{{invoice_id}}", "inv"})
}, .repairs = {{m_not_authorized, {exec(.call = refresh_billing_token)}}});

Combined:

// on-demand: enqueued via run("recount_todos")
task("recount_todos", {
  sqlite_query({"todos_db", "recount"})
}, .accepts = {"user_id"});

// recurring: runs on schedule, no caller
task("daily_digest", {
  sqlite_query({"todos_db", "digest"}),
  emit("digest_ready")
}, .cron = "0 8 * * *");

Modules and Composition

The root main.c defines the app with the mach() macro. A module is declared with module(name) in a name/name.c file. A module owns its own resources, databases, migrations, tasks, event contracts, and middleware. Compose by #includeing a module's .c file.

A module owns the files in its folder, which are seeded into its context at startup. See Assets and Context.

module(name): declares a module.

// todos/todos.c
module(todos){
  // resources, databases, tasks, subscribers ...
}

middleware(steps): registers shared steps that run on every request to a resource in the same module. Cross-cutting setup like session loading or tenant resolution lives here.

mach(){ middleware(session()); /* modules, resources, ... */ }

error(...) / repair(...): module-scoped error and repair handlers (see Error and Repair Pipelines). They cover resources in the same module; a resource's own .errors/.repairs override them for the same code.

Pipeline composition. A request runs the resource's .all steps first, then the module's middleware(), then the verb pipeline.

// main.c: root config
#include <mach.h>
#include <session_auth.h>
#include "todos/todos.c"

mach(){
  middleware(session());

  resource("home", "/", .get = {mustache("home")});
}

// todos/todos.c: session loads, resources require login
#include <mach.h>
#include <sqlite.h>
#include <session_auth.h>

module(todos){
  middleware(logged_in());
  middleware(session());

  resource("todos", "/todos",
    .get = { sqlite_query({"todos_db", "get_todos", "todos_data"}), mustache("todos") },
    .post = { input({"title", m_not_empty}), sqlite_query({"todos_db", "create_todo"}), redirect("todos") }
  );

  resource("todo", "/todos/:id",
    .all = {
      input({"id", m_positive})
    },
    .delete = { sqlite_query({"todos_db", "delete_todo", .must_exist = true}), redirect("todos") }
  );
}

For GET /todos/5 the executed order is: input({"id", ...}) (resource .all), logged_in(), session() (module middleware), then the verb pipeline sqlite_query({"get_todo", ..., .must_exist = true}), mustache("todo").

Complete module file. A module registers the same kinds of things the root does. A blogs/blogs.c:

#include <mach.h>
#include <sqlite.h>

module(blogs){
  sqlite_database(
    "blog_db",
    "file:blogs.db?mode=rwc",
    {"create_blogs_table", "create_comments_table"}
  );

  resource("blog", "/blogs/:id",
    .get = {...}
  );
}

Bring it into scope by #includeing its .c file from main.c:

// main.c
#include <mach.h>
#include "blogs/blogs.c"

mach(){}

A typical project layout:

├── todos/ # todos module (folder + matching .c)
│   ├── todos.c # module(todos){ ... }
│   ├── todos.mustache.html # → todos
│   ├── create_todos_table.sql # → todos
│   └── get_todos.sql # → todos
├── activity/ # activity module
│   └── activity.c
├── home.mustache.html # → main (also the shared layout)
├── public/ # static files, served directly
│   └── favicon.png
└── main.c # mach() { ... }, composes the rest

---

Module Reference

Bundled modules. Activate each by #includeing its header.

• htmx
• datastar
• tailwind
• session_auth
• Database engines

htmx

Activate with #include <htmx.h>. Serves the htmx runtime as the {{>htmx}} partial, and sets the is_htmx context flag on requests carrying the HX-Request header. Pair the flag with .if_context/.unless_context to return a fragment to htmx and a full page to a direct visit, or use hx-boost to upgrade ordinary links and forms into AJAX swaps.

#include <mach.h>
#include <htmx.h>

mach(){
  resource("todos", "/todos",
    .get = {
      sqlite_query({"todos_db", "get_todos", "todos_data"}),
      mustache("todos_fragment", .if_context = "is_htmx"),
      mustache("todos_page", .unless_context = "is_htmx")
    }
  );
}

Include the runtime once in the page <head>:

<head>{{>htmx}}</head>
<body hx-boost='true'>...</body>

datastar

Activate with #include <datastar.h>. Serves the Datastar runtime as the {{>datastar}} partial and provides datastar_sse() for pushing reactive fragment and signal patches over an SSE channel. A page opens an SSE connection (a resource .sse channel); pipelines push patches to that channel, and Datastar applies them in the DOM.

datastar_sse() renders a template and patches it into the page by CSS selector. The first value is the channel (supports {{interpolation}}).

.channel (by order): channel to push to.

datastar_sse("todos:{{user_id}}", .target = "#todo-list", .mode = mode_append, .elements = {"todo_row"})

.target: CSS selector for the element to patch; supports {{interpolation}}.

.target = "#todo-{{id}}"

.mode: how the rendered fragment is applied to the target (a datastar_mode).

.mode = mode_replace

.elements: a render_config (a template asset name) producing the fragment to patch in. Not required for mode_remove.

.elements = {"todo_row"}

.signals: context key holding signal state to merge into the client store.

.signals = "ui_state"

.js: JavaScript to execute on the client.

.js = "window.scrollTo(0, document.body.scrollHeight)"

Patch modes (datastar_mode): mode_outer, mode_inner, mode_replace, mode_prepend, mode_append, mode_before, mode_after, mode_remove.

Worked example: a POST inserts a row, returns it with RETURNING, appends it to every connected client's list.

resource("todos", "/todos",
  // Each browser opens this channel and listens for patches.
  .sse = {"todos:{{user_id}}"},

  .post = {
    input({"title", m_not_empty}),
    // RETURNING gives the new row back; capture it under "todo".
    sqlite_query({"todos_db", "insert_todo", "todo", .must_exist = true}),
    // Patch the new row into the list for everyone on the channel.
    datastar_sse("todos:{{user_id}}",
      .target = "#todo-list",
      .mode = mode_append,
      .elements = {"todo_row"}
    )
  }
);

Removing an element needs only a selector:

datastar_sse("todos:{{user_id}}", .target = "#todo-{{id}}", .mode = mode_remove)

Datastar sets a context flag on requests it originates, usable with .if_context.

Include the runtime once in the page <head>:

<head>{{>datastar}}</head>

tailwind

Activate with #include <tailwind.h>. Compiles Tailwind utility classes used across the project's templates and serves the stylesheet as the {{>tailwind}} partial. Use Tailwind classes directly in templates; no build step or config file required.

<head>{{>tailwind}}</head>
<body class='bg-gray-950 text-white min-h-screen'>
  <h1 class='text-3xl font-bold text-center mb-8'>Vote for which is roundest</h1>
</body>

session_auth

Activate with #include <session_auth.h>. Cookie-based authentication as pipeline steps. session() loads the current user record into context from the session cookie; run it as middleware() in each module whose pipelines need to know who is signed in. logged_in() guards a resource, redirecting anonymous visitors to the login page. login(), logout(), and signup() perform the corresponding actions. The login page template is the asset named login.

session(): loads the current user into context from the session cookie. Use as middleware.

middleware(session());

logged_in(): requires an authenticated session; redirects to login otherwise. Use in a resource .all.

resource("todos", "/todos", .all = {logged_in()}, .get = { ... });

login() / logout() / signup(): authentication actions for the corresponding verb pipelines.

resource("login", "/login",
  .get = { mustache("login") },
  .post = { login() }
);
resource("logout", "/logout", .post = { logout() });
resource("signup", "/signup",
  .get = { mustache("signup") },
  .post = { signup() }
);

Combined: load the session in the module whose resources it gates, then read user fields in that module's templates.

// todos/todos.c
#include <mach.h>
#include <session_auth.h>

module(todos){
  middleware(logged_in());
  middleware(session());

  resource("todos", "/todos", .get = { mustache("todos") });
}

// main.c: login/logout live at the root
#include <mach.h>
#include <session_auth.h>
#include "todos/todos.c"

mach(){
  resource("login", "/login", .get = {mustache("login")}, .post = {login()});
  resource("logout", "/logout", .post = {logout()});
}

<!-- once a session() has loaded the user, templates can read it -->
{{#user}}<span>Hi, {{short_name}}</span>{{/user}}

Database engines

Each engine is its own module: #include its header, then use <engine>_database(...) to register and <engine>_query({...}) as a pipeline step. They share database_config and query_config from Databases and query; only .connect is engine-specific.

#include <sqlite.h> // sqlite_database("...", "file:app.db?mode=rwc", ...); sqlite_query({...});
#include <postgres.h> // postgres_database("...", "postgres://...", ...); postgres_query({...});
#include <mysql.h> // mysql_database("...", "mysql://...", ...); mysql_query({...});
#include <redis.h> // redis_database("...", "redis://...", ...); redis_query({...});
#include <duckdb.h> // duckdb_database("...", "duckdb:analytics.db", ...); duckdb_query({...});

Static Files

Files in public/ are served directly. Reference them in templates with {{asset:filename}}, which resolves to a content-checksummed, cache-busted URL with immutable cache headers. Updates invalidate caches automatically; unchanged files cache forever.

public/
├── favicon.png
├── styles.css
└── logo.svg

<link rel='icon' href='{{asset:favicon.png}}'>
<link rel='stylesheet' href='{{asset:styles.css}}'>
<img src='{{asset:logo.svg}}' alt='Logo'>

This differs from assets like SQL and HTML templates, which are embedded from files anywhere in the project and seeded into context for steps to read by key (see Assets and Context). public/ holds opaque files served to the browser.

External Dependencies

Drop third-party C libraries into /vendor; MACH compiles and links them with the app. Call into them from exec()/worker() steps. Memory returned by a library that must be freed manually is registered with defer_free() so it is reclaimed when the request completes (see memory).

vendor/
└── cmark/
    ├── cmark.c
    └── cmark.h

#include <mach.h>
#include "vendor/cmark/cmark.h"

void render_markdown(){
  worker(^(){
    auto md = get("markdown");
    auto html = cmark_markdown_to_html(md, strlen(md), 0);
    defer_free(html); // library-owned pointer
    set("html_content", html);
  });
}

For dependencies that aren't plain source (system packages, build tooling), provide a custom Dockerfile. MACH builds from it instead of the default image.

---

Architecture

• Data-Oriented Pipelines
• Multi-Reactor Architecture
• Safe by Default

Data-Oriented Pipelines

mach() runs once at boot, alongside each module's constructor. Registration calls (resource(), sqlite_database(), task(), middleware(), publish(), etc.) are processed into an execution graph with precompiled pipelines, queries, and templates. Each incoming request 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 is set in compose.yml.

• Request reactors handle HTTP traffic; each gets a dedicated CPU core and event loop.
• Task reactors handle background work; each gets a 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.

A worker() step dispatches work to the shared pool, releasing the reactor; the pipeline resumes on the original reactor when the call completes. exec() runs inline on the reactor for short, non-blocking logic. run() adds jobs to the task database, picked up by task reactors. Tasks can call run() themselves.

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 (use allocate() and defer_free() from the Imperative API for raw buffers), avoiding 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 exceeding their memory limit (default 5MB, configurable in compose.yml) abort with a 500, mitigating OOM denial-of-service.

SQL Injection Prevention

Interpolations like {{user_id}} inside a query's SQL (whether the SQL comes from a .sql file or a context()-registered string) are bound as parameters in prepared statements, preventing SQL injection at the framework level.

XSS Prevention

The mustache() and mdm() steps auto-escape context values, so malicious input is rendered as text. Raw HTML requires explicit opt-in via Mustache's standard unescape syntax: {{{field}}} or {{&field}}.

CSRF Prevention

State-changing requests are verified against a per-session CSRF token. Emit the token with {{csrf:input}} (hidden form field) or {{csrf:token}} (value for query strings); MACH sets it on an httponly, secure, samesite cookie and rejects requests whose token does not match. See Templates.

---

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, module boundaries), so it reasons about the application's actual execution graph rather than the source text alone.

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 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

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 a minimal 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

Ships with integrated 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.