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What is MCP?

Model Context Protocol (MCP) is an open standard that lets AI agents connect to external tools and data sources. MCPs give agents capabilities like browsing the web, querying databases, or interacting with third-party APIs.

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Built-in MCPs

Twill automatically configures these MCP servers for all tasks:
MCP ServerCapabilities
GitHubRead repository info, issues, and pull requests
PlaywrightBrowser automation and web interaction
Context7Up-to-date documentation for libraries
LinearRead and update Linear issues (when connected)

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Adding Custom MCPs

You can add custom MCP servers by creating a .mcp.json file in your repository root. Twill will detect this file and make those servers available to the agent.

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Configuration Format

Create a .mcp.json file with this structure: 
{
  "mcpServers": {
    "my-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "my-mcp-server@latest"]
    }
  }
}

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Server Types

MCP supports two connection types:
TypeDescriptionExample
stdioRuns a local commandnpx, uvx, or any CLI tool
httpConnects to a remote HTTP endpointhttps://mcp.example.com

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Example: Adding a Database MCP

{
  "mcpServers": {
    "postgres": {
      "type": "stdio",
      "command": "uvx",
      "args": ["postgres-mcp", "--access-mode=readonly"],
      "env": {
        "DATABASE_URI": "${DATABASE_URL}"
      }
    }
  }
}
Use environment variable syntax (${VAR_NAME}) to reference secrets. Configure these in your repository environment settings.

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Example: Adding an HTTP MCP

{
  "mcpServers": {
    "my-api": {
      "type": "http",
      "url": "https://mcp.myservice.com",
      "headers": {
        "Authorization": "Bearer ${MY_API_TOKEN}"
      }
    }
  }
}