iii-getting-started

Getting Started with iii

iii replaces your API framework, task queue, cron scheduler, pub/sub, state store, and observability pipeline with a single engine and three primitives: Function, Trigger, Worker.

Step 1: Install the Engine

curl -fsSL https://install.iii.dev/iii/main/install.sh | sh

Verify it installed:

iii --version

Step 2: Create a Project

iii project init my-app              # barebones project
iii project init my-app -t harness   # or: the harness template (agent + console UI)
cd my-app

iii project init --learn-iii scaffolds the harness template and starts it in one step; the installer offers the same when you answer "y" at its prompt. iii project init --template quickstart scaffolds the Quickstart with a Python and a TypeScript worker.

Step 3: Start the Project

iii compose --namespace dev --up --file worker-compose.yaml

The file's engine: section starts the engine; containers: starts project workers. The engine commonly listens on ws://localhost:49134. Keep this foreground supervisor running.

--namespace dev names the daemon and becomes III_NAMESPACE for every worker it starts, so your workers register and call each other in dev; that is why the iii trigger commands below pass -n dev. Engine-owned functions (engine::*, configuration::*) stay in default, and SDK calls to them resolve there without a namespace (see iii-sdk-reference).

Step 4: Install the SDK

Pick your language:

# TypeScript / Node.js
pnpm add iii-sdk @iii-dev/helpers

# Python
pip install iii-sdk iii-helpers

# Rust
cargo add iii-sdk iii-helpers

Step 5: Write Your First Worker

TypeScript

import { registerWorker, TriggerAction } from "iii-sdk";
import { Logger } from "@iii-dev/helpers/observability";

const iii = registerWorker(process.env.III_URL ?? "ws://localhost:49134");

iii.registerFunction(
  "hello::greet",
  async (input) => {
    const logger = new Logger();
    const name = input?.name ?? "world";
    logger.info("Greeting user", { name });
    return { message: `Hello, ${name}!` };
  },
  { description: "Greet a user by name" },
);

iii.registerTrigger({
  type: "http",
  function_id: "hello::greet",
  config: { api_path: "/hello", http_method: "POST" },
});

Python

from iii import register_worker, InitOptions
from iii_helpers.observability import Logger

iii = register_worker(address="ws://localhost:49134", options=InitOptions(worker_name="hello-worker"))

def greet(data):
    logger = Logger()
    name = data.get("name", "world") if isinstance(data, dict) else "world"
    logger.info("Greeting user", {"name": name})
    return {"message": f"Hello, {name}!"}

iii.register_function("hello::greet", greet, description="Greet a user by name")
iii.register_trigger({"type": "http", "function_id": "hello::greet", "config": {"api_path": "/hello", "http_method": "POST"}})

Rust

use iii_sdk::{register_worker, InitOptions, RegisterFunction};
use iii_sdk::protocol::RegisterTriggerInput;
use iii_helpers::observability::Logger;
use serde_json::json;

let iii = register_worker("ws://127.0.0.1:49134", InitOptions::default());

iii.register_function(
    "hello::greet",
    RegisterFunction::new(|input: serde_json::Value| -> Result<serde_json::Value, iii_sdk::Error> {
        let logger = Logger::new();
        let name = input["name"].as_str().unwrap_or("world");
        logger.info("Greeting user", Some(json!({ "name": name })));
        Ok(json!({ "message": format!("Hello, {}!", name) }))
    }).description("Greet a user by name"),
);

// Deprecated since 0.25, still how you bind to the http worker: compiles with a warning.
#[allow(deprecated)]
iii.register_trigger(RegisterTriggerInput::new(
    "http",
    "hello::greet",
    json!({ "api_path": "/hello", "http_method": "POST" }),
))?;

registerTrigger logs a one-time deprecation warning in iii 0.25. It keeps working, and it is still the way to bind to the http, cron, queue, state, stream, and pub/sub workers, which have not moved to source functions yet. To run a function after another one, use iii.observe (see iii-observe).

Step 6: Test It

The http trigger type comes from the http worker. Add it once through the running Compose daemon, then call your endpoint:

iii trigger -n dev compose::add worker=http

curl -X POST http://localhost:3111/hello \
  -H "Content-Type: application/json" \
  -d '{"name": "iii"}'

Expected response:

{ "message": "Hello, iii!" }

Add Existing Workers

To add a capability that already exists, browse https://workers.iii.dev/ and add it through the running Compose daemon:

iii trigger -n dev compose::add worker=state
iii trigger -n dev compose::add worker=queue
iii trigger -n dev compose::add worker=image-resize@0.1.2

compose::add resolves dependencies, writes exact versions to worker-compose.yaml, and restarts the affected project. A local worker can be declared as a path:// container or added by path.

Install Agent Skills

Get all iii skills for your AI coding agent:

npx skills add iii-hq/iii/skills

Skills teach your agent the top-level iii model: functions, triggers, workers, observers, registry access, SDKs, engine configuration, architecture patterns, and error handling. Worker-backed capabilities live with the worker docs and registry entries.

Adapting This Pattern

• Add more functions to the same worker: each gets its own registerFunction + registerTrigger

calls

• Use :: separator for function IDs to namespace them: orders::create, orders::validate
• Add cron triggers with { type: 'cron', config: { expression: '0 0 9 * * * *' } } (7-field: sec

min hour day month weekday year)

• Add queue triggers with { type: 'durable:subscriber', config: { topic: 'my-queue' } }
• Use iii.trigger() to invoke other functions from within a function
• Use iii.observe({ function_id: "hello::greet" }, "audit::record") to run a registered function

after every successful call of another one (see iii-observe)

• Use state::get / state::set to persist data across function calls
• Use iii trigger -n <daemon> compose::add worker=<name> when the capability already exists in

the worker registry

Recommended Next Steps

After getting your first worker running:

1. Register functions, triggers, and workers: see iii-core-primitives
2. Observe functions and engine events: see iii-observe
3. Choose the right SDK APIs: see iii-sdk-reference
4. Configure the engine: see iii-engine-config
5. Explore backend patterns: see iii-architecture-patterns
6. Handle failures well: see iii-error-handling

Key Resources

• Quickstart Guide
• SDK Reference: Node.js
• SDK Reference: Python
• SDK Reference: Rust
• Compose
• Configuration
• Console
• Observers
• Upgrading from 0.24.x
• Every docs page is also available as Markdown by adding a .md suffix to its URL.

Pattern Boundaries

• For function and trigger registration patterns, worker creation, worker registry access, trigger

payload schemas, invocation modes, channels, custom triggers, and HTTP-invoked functions, prefer iii-core-primitives

• For observing functions and engine events, and for migrating off registerTrigger, prefer

iii-observe

• For language-specific SDK APIs, prefer iii-sdk-reference
• For engine configuration, prefer iii-engine-config
• For worker-backed HTTP, cron, queue, pubsub, state, stream, and observability behavior, use the matching worker page on https://workers.iii.dev/
• Stay with iii-getting-started for installation, initial setup, and first-worker guidance

When to Use

• Use this skill when the task is about installing iii, creating a new project, or writing a first

worker.

• Triggers when the request asks for setup help, quickstart guidance, or getting started with iii.

Boundaries

• Never use this skill as a generic fallback for unrelated tasks.
• You must not apply this skill when a more specific iii skill is a better fit.
• Always verify environment and safety constraints before applying examples from this skill.