Quick start#

Create an app#

bun create janux my-app
cd my-app
bun install
bun run dev

bunx create-janux my-app is the same command. Prefer starting from a complete app? Any example works as a template:

bun create janux my-shop --example shop

Requirements: Bun ≥ 1.3. No other global tooling.

What the dev server gives you#

janux dev ready
  → app:      http://localhost:3000/
  → manifest: http://localhost:3000/_janux/manifest
  → agent:    http://localhost:3000/_janux/agent

Open the app: a counter island and an agent panel. Then open the manifest — that JSON is your app as an agent sees it, generated from the same components. The two views are never out of sync because there is only one definition.

curl localhost:3000/_janux/manifest

Make your first change#

Edit src/components/Counter.tsx and add an intent:

TSXsrc/components/Counter.tsx

intents: {
  inc: intent({
    description: 'Increment the counter',
    input: schema({ by: int().default(1) }),
    run: ({ state, input }) => (state.count += input.by),
  }),
  double: intent({
    description: 'Double the counter',
    run: ({ state }) => (state.count *= 2),
  }),
},

Save. Three things happen at once: the view hot-reloads, counter.double appears in the manifest, and the copilot can call it — no registration, no schema written twice.

Turn on the copilot#

The agent panel needs a model. Set one environment variable:

# option 1: pick the model explicitly
JANUX_MODEL="anthropic/claude-fable-5" bun run dev

# option 2: just give it a provider key and let it choose
ANTHROPIC_API_KEY=sk-... bun run dev

Also supported: OPENAI_API_KEY, GOOGLE_GENERATIVE_AI_API_KEY, OPENROUTER_API_KEY. Resolution order is defineAgent({ model }) → JANUX_MODEL → provider-key sniffing → a setup card. Without any of them the app still boots and tells you exactly which variable to set.

Now ask the copilot "double the counter twice" and watch the view update — the agent called the same intent your button calls.

Ship it#

bun run build     # bundles client assets
bun run start     # production server on Bun

Apps with no islands (or "output": "static") build to a folder of HTML you can host anywhere — see CLI and deployment.

Next: Project structure · Mental model