Mods

One typed value, exported from src/mod.tsx. Not a class, not an activation function, not a manifest plus a runtime.

import { function command<TId extends string>(commandValue: CommandInput<TId>): Command<TId>
Declare an action the user runs from the command palette or a keybinding.

Reach for this when a person triggers the behavior. The `title` is what they
read in the palette, `category` groups the entry, and `when` decides whether
it shows up at all. The handler takes no argument, only a context.

Two neighbours are easy to confuse. `slashCommand` is also user-triggered,
but it is typed inside a chat session and receives free text plus the live
AI session. `tool` is not user-triggered at all, the model decides to call
it mid-turn.

The result goes in the mod's top-level `commands` array, alongside any slash
commands. The `id` is the address a keybinding or a `command:` hook targets,
so keep it stable.
@categoryAuthoringcommand, function defineMod<const TMod extends ModDefinition>(definition: TMod & ValidateModHooks<TMod>): Mod
The entry point of the SDK. A mod's module default-exports one `defineMod`
call and nothing else.

The returned value is data. It registers nothing, starts nothing, and
touches no host state. The host folds it twice. At build time it runs the
module in a throwaway sandbox and reads the value to derive the serializable
manifest. At runtime it folds the same value again to wire your handlers
into their lanes: ext-host for commands, tools, effects, and hooks; the
sandboxed renderer for views and widgets.

That double fold is why the module must be pure. It is re-executed to
produce the manifest, so anything at the top level, a file read, a network
call, a timer, a `console` line, runs during a build with no host attached.
Put behavior inside handlers: `run`, `activate`, `handle`.

The `ValidateModHooks` constraint makes the call fail to typecheck when a
`hook.beforeAction` targets an action that is neither a known host action
nor `command:` plus one of this mod's own command ids.
@example```ts
export default defineMod({
  metadata: {
    displayName: 'Review',
    description: 'Review helpers for the current change.',
  },
  commands: [
    command({ id: 'review.open', title: 'Review: Open', run: openPanel }),
    slashCommand({ id: 'review', description: 'Review this change', run: review }),
  ],
  ai: {
    tools: [reviewTool],
  },
});
```@categoryAuthoringdefineMod } from '@modular/sdk';

export default 
defineMod<{
    readonly metadata: {
        readonly displayName: "Hello";
        readonly description: "A first mod";
    };
    readonly commands: readonly [Command<string>];
}>(definition: {
    readonly metadata: {
        readonly displayName: "Hello";
        readonly description: "A first mod";
    };
    readonly commands: readonly [Command<string>];
}): Mod
The entry point of the SDK. A mod's module default-exports one `defineMod`
call and nothing else.

The returned value is data. It registers nothing, starts nothing, and
touches no host state. The host folds it twice. At build time it runs the
module in a throwaway sandbox and reads the value to derive the serializable
manifest. At runtime it folds the same value again to wire your handlers
into their lanes: ext-host for commands, tools, effects, and hooks; the
sandboxed renderer for views and widgets.

That double fold is why the module must be pure. It is re-executed to
produce the manifest, so anything at the top level, a file read, a network
call, a timer, a `console` line, runs during a build with no host attached.
Put behavior inside handlers: `run`, `activate`, `handle`.

The `ValidateModHooks` constraint makes the call fail to typecheck when a
`hook.beforeAction` targets an action that is neither a known host action
nor `command:` plus one of this mod's own command ids.
@example```ts
export default defineMod({
  metadata: {
    displayName: 'Review',
    description: 'Review helpers for the current change.',
  },
  commands: [
    command({ id: 'review.open', title: 'Review: Open', run: openPanel }),
    slashCommand({ id: 'review', description: 'Review this change', run: review }),
  ],
  ai: {
    tools: [reviewTool],
  },
});
```@categoryAuthoringdefineMod({
  
metadata: {
    readonly displayName: "Hello";
    readonly description: "A first mod";
}metadata: { displayName: "Hello"displayName: 'Hello', description: "A first mod"description: 'A first mod' },
  commands: readonly [Command<string>]commands: [
    command<string>(commandValue: CommandInput<string>): Command<string>
Declare an action the user runs from the command palette or a keybinding.

Reach for this when a person triggers the behavior. The `title` is what they
read in the palette, `category` groups the entry, and `when` decides whether
it shows up at all. The handler takes no argument, only a context.

Two neighbours are easy to confuse. `slashCommand` is also user-triggered,
but it is typed inside a chat session and receives free text plus the live
AI session. `tool` is not user-triggered at all, the model decides to call
it mid-turn.

The result goes in the mod's top-level `commands` array, alongside any slash
commands. The `id` is the address a keybinding or a `command:` hook targets,
so keep it stable.
@categoryAuthoringcommand({
      id: stringid: 'hello.greet',
      title: stringtitle: 'Greet',
      run: (ctx: CommandContext) => Awaitable<unknown>run: async ctx: CommandContextctx => {
        await ctx: CommandContextctx.ui: UiCapability
Notifications, dialogs, quick input, and progress.ui.UiCapability.notification: UiNotificationCapabilitynotification.UiNotificationCapability.info(request: UiNotificationRequest): Promise<UiActionResult>info({ UiNotificationRequest.message: stringmessage: 'Hello.' });
      },
    }),
  ],
});

The shape of Mod

defineMod takes metadata and one array per contribution kind. Every key is optional except the ones your mod actually uses. Each links to the section that covers it.

Key	Covered in
metadata	Metadata
commands	Commands · Slash commands
keybindings	Keybindings
tools agents prompts	AI
views widgets walkthroughs	Surfaces
events hooks conditions effects auth system	Connections
state	State
editor canvas	Editing
theme ui	Appearance
checks	Checks

Full member list: Mod.

Why a value and not a lifecycle

The host folds the value into a manifest at build time and into live wiring at runtime. Two consequences worth knowing:

• There is no separate manifest file to keep in sync with your code.
• There is no second schema language. Your TypeScript types are the contract, and the authoring compiler generates the runtime validators from them.