> ## Documentation Index
> Fetch the complete documentation index at: https://docs.twill.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP servers

> Built-in MCP tools from your integrations, plus custom servers via a .mcp.json in your repo.

Agents reach external systems through [MCP](https://modelcontextprotocol.io/) tools and CLIs available in the sandbox.

## Built in

* **Context7** — up-to-date library documentation, available on every task
* **Linear** and **Notion** — MCP tools appear automatically when the [integration](/integrations/overview) is connected
* **GitHub** — via the authenticated `gh` CLI (not MCP)
* **Browser automation** — via the `agent-browser` CLI, which powers UI verification

## Custom servers

Add a `.mcp.json` at your repo's root and the coding agents pick it up:

```json .mcp.json theme={"theme":"github-dark"}
{
  "mcpServers": {
    "my-tool": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "my-mcp-server@latest"]
    },
    "database": {
      "type": "stdio",
      "command": "uvx",
      "args": ["postgres-mcp", "--access-mode=readonly"],
      "env": { "DATABASE_URI": "${DATABASE_URL}" }
    },
    "internal-api": {
      "type": "http",
      "url": "https://mcp.myservice.com",
      "headers": { "Authorization": "Bearer ${MY_API_TOKEN}" }
    }
  }
}
```

* `stdio` servers run as a command inside the sandbox (`npx`, `uvx`, …).
* `http` servers are remote endpoints.
* `${VAR_NAME}` references resolve from your workspace [environment variables](/environment#environment-variables--secrets), so secrets stay out of the repo.