buttercup.sh

Buttercup.sh is a free, hands-on place to learn how AI agents work by building one directly in the page. It offers a friendly agent lesson every week, and each lesson adds a capability, from a first completion call to tools, browser control, vision, and evals. Users can begin anywhere, and every past lesson is waiting in the archive. No sign up is required.

To use it, users open KEYS, choose a provider, and paste an API key. The browser keeps the key in localStorage and sends requests directly to the provider. A suggested first prompt is “scaffold a blocks.ai research agent, then run it”, and the agent's files appear in the workspace. Commands like /undo roll back the latest file and conversation changes, and /help is always nearby.

The tool includes a LiveCodes compiler that turns JSX, Vue, Svelte, Sass, TypeScript, Python, and more than 80 other formats into a page you can preview and photograph. It runs in the browser and loads the SDK from a CDN and the playground from livecodes.io. Before running the SDK, the harness verifies its pinned version and SHA-256 hash. SAVE checks the key against the provider's model list without spending tokens, and the lamp turns READY when the provider accepts the key. At compact at, the harness replaces the conversation with a handover summary, leaving workspace files alone, and /undo restores the full context.