Install Belgie

Install Belgie to build MCP App UIs for Claude, ChatGPT, and other MCP Apps hosts from a Python MCP server, or to give an AI agent a JavaScript and TypeScript sandbox. The base package embeds a Deno-powered runtime, so neither path needs a separate Node.js install.

Install for MCP Apps

Most projects start with the MCP and CLI extras:

uv add "belgie[mcp,cli]"

Then follow MCP Apps to declare widget dependencies and register a tool.

Install the runtime

uv add belgie

Belgie supports Python 3.12 through 3.14. Install the base package alone when you want direct script execution or plan to add an integration later.

Choose an integration

Install only the integration dependencies your project uses.

Extra	Adds	Use it when you need
`cli`	`typer`, `rtoml`, and `tomlkit`	Project dependency commands such as `belgie lock` and `belgie run`.
`mcp`	MCP server and MCP Apps types	Python MCP tools with `BelgieExtension`.
`pydantic-ai`	Pydantic AI with the OpenAI provider	`BelgieSandbox`.
`langchain`	LangChain	`BelgieMiddleware`.

For an agent project, install the framework you use:

uv add "belgie[pydantic-ai]"
uv add "belgie[langchain]"

TypeScript package dependencies

The Python runtime does not require Node.js. MCP widget projects still declare their React, Vite, and @belgie/mcp dependencies in [tool.belgie.dependencies]; Belgie resolves and runs them through its embedded Deno environment.

Verify the installation

Verify the runtime before adding an agent or UI integration:

uv run python - <<'PY'
import asyncio

from belgie import Runtime, Script


async def main() -> None:
    async with Runtime() as runtime:
        result = await runtime(Script("export default () => ({ status: 'ok' });"))()
    print(result)


asyncio.run(main())
PY

The command should print {'status': 'ok'}. If it fails, confirm that you are running it inside the project environment where Belgie was installed, then check Troubleshooting.

Optional editor skill

If you use an editor or coding agent that supports the use-belgie skill, install the optional skill with:

uvx library-skills install

The skill is optional. It is not required to import or run Belgie.