---
name: build-a-buildy-app
description: Create, host, and iterate on a personal interactive web app with Buildy — a real URL, persistent storage, and an MCP or HTTP API — from any agent.
---

# Build a Buildy app

Buildy turns a natural-language description into a hosted web app with a real URL and a database. Use it from any MCP-capable client or over plain HTTP; the first app is free with no signup.

## When to use this

Reach for Buildy when the user wants a small app that outlives the chat: a tracker, a dashboard, a form, a personal tool. Buildy gives it a persistent URL, storage, and an API your agent can keep using and updating across sessions.

## Two surfaces

- **MCP** (Claude, ChatGPT, Cursor, Claude Code, and more): add `https://app.buildy.so/mcp` as an MCP server, then call the tools. Per-client setup strings: https://buildy.so/clients.txt
- **HTTP**: `POST https://app.buildy.so/app` with the app source. Full contract: https://app.buildy.so/.well-known/openapi.json

## Build flow (MCP)

1. `create_app` — author a new app from a name plus source (an ES module for logic + UI/styles). The response carries the live URL.
2. `update_app` — iterate on the source.
3. `query_app` / `mutate_app` — read and write the app's stored state.
4. `share_app` / `set_remixable` — share with people or let any visitor fork the URL.

Generated app HTML talks to its backend through the injected `window.buildy` API — never raw `fetch`.

## Learn more

- Start here: https://buildy.so/start.md
- Full build manual: https://buildy.so/llms-full.txt
- Design rules (avoid the generic AI-app look): https://buildy.so/design.md

## Auth

Anonymous app creation needs no token — the first app is free, with a 7-day TTL until it is claimed. To claim and manage apps, mint a `bld_user_*` token via device pairing (`POST https://app.buildy.so/api/pair/start`, then poll) or by signing in. See https://buildy.so/auth.md.