Using Iii

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# Functions


{/* TODO: Re-link worker references to https://workers.iii.dev/workers/<name> once the Worker Docs migration ships. */}

## Invoking functions

A function runs when a trigger fires. The same function can be invoked from many trigger types at
once (direct CLI calls, an HTTP route, and a cron schedule, for example) without changing the
handler.

<Note>
  Some trigger types are: [`iii trigger`](./cli), [`worker.trigger`](./triggers),
  iii-http,
  iii-cron,
  iii-queue,
  iii-state,
  iii-stream.
</Note>

## Register a function

Inside a worker, `worker.registerFunction(id, handler)` makes a function callable from anywhere in
the iii system. The `id` follows the `service::name` form; the handler receives the call's payload
and returns the result.

<Tabs>
  <Tab title="Node / TypeScript">
    ```typescript
    import { registerWorker } from "iii-sdk";

    const worker = registerWorker(process.env.III_URL);

    worker.registerFunction("math::add", async (payload: { a: number; b: number }) => {
      return { c: payload.a + payload.b };
    });
    ```

  </Tab>
  <Tab title="Python">
    ```python
    import os
    from iii import register_worker, InitOptions

    worker = register_worker(
        os.environ.get("III_URL"),
        InitOptions(worker_name="math-worker"),
    )

    def add_handler(payload: dict) -> dict:
        return {"c": payload["a"] + payload["b"]}

    worker.register_function("math::add", add_handler)
    ```

  </Tab>
  <Tab title="Rust">
    ```rust
    use iii_sdk::{InitOptions, RegisterFunction, register_worker};

    let url = std::env::var("III_URL").expect("III_URL must be set");
    let worker = register_worker(&url, InitOptions::default());

    worker.register_function(RegisterFunction::new("math::add", |input: AddInput| {
        Ok(serde_json::json!({ "c": input.a + input.b }))
    }));
    ```

  </Tab>
</Tabs>

## Define request and response formats

Functions can carry JSON Schemas for their request payload and response shape. The schemas are
stored with the function and feed the iii console and the agent-readable skills.

<Note>
  Runtime validation is not yet supported. Attached schemas are metadata only; the engine does not
  reject payloads or responses that don't match. Treat the schemas as contract documentation for
  callers, agents, and the console until validation lands.
</Note>

<Note>
  For how to attach schemas when registering a function, see [Creating Workers /
  Functions](../creating-workers/functions#attach-request-and-response-schemas).
</Note>

## Invoke a function

<Note>
  For how to call a registered function from worker code or the terminal (with optional delivery
  actions like fire-and-forget or queue-routed), see
  [Triggers / Call a function directly](./triggers#call-a-function-directly).
</Note>