deer-flow/backend/docs/MCP_SERVER.md

# MCP (Model Context Protocol) Configuration

DeerFlow supports configurable MCP servers and skills to extend its capabilities, which are loaded from a dedicated `extensions_config.json` file in the project root directory.

## Setup

1. Copy `extensions_config.example.json` to `extensions_config.json` in the project root directory.
   ```bash
   # Copy example configuration
   cp extensions_config.example.json extensions_config.json
   ```
   
2. Enable the desired MCP servers or skills by setting `"enabled": true`.
3. Configure each server’s command, arguments, and environment variables as needed.
4. Restart the application to load and register MCP tools.

## OAuth Support (HTTP/SSE MCP Servers)

For `http` and `sse` MCP servers, DeerFlow supports OAuth token acquisition and automatic token refresh.

- Supported grants: `client_credentials`, `refresh_token`
- Configure per-server `oauth` block in `extensions_config.json`
- Secrets should be provided via environment variables (for example: `$MCP_OAUTH_CLIENT_SECRET`)

Example:

```json
{
   "mcpServers": {
      "secure-http-server": {
         "enabled": true,
         "type": "http",
         "url": "https://api.example.com/mcp",
         "oauth": {
            "enabled": true,
            "token_url": "https://auth.example.com/oauth/token",
            "grant_type": "client_credentials",
            "client_id": "$MCP_OAUTH_CLIENT_ID",
            "client_secret": "$MCP_OAUTH_CLIENT_SECRET",
            "scope": "mcp.read",
            "refresh_skew_seconds": 60
         }
      }
   }
}
```

## Custom Tool Interceptors

You can register custom interceptors that run before every MCP tool call. This is useful for injecting per-request headers (e.g., user auth tokens from the LangGraph execution context), logging, or metrics.

Declare interceptors in `extensions_config.json` using the `mcpInterceptors` field:

```json
{
  "mcpInterceptors": [
    "my_package.mcp.auth:build_auth_interceptor"
  ],
  "mcpServers": { ... }
}
```

Each entry is a Python import path in `module:variable` format (resolved via `resolve_variable`). The variable must be a **no-arg builder function** that returns an async interceptor compatible with `MultiServerMCPClient`’s `tool_interceptors` interface, or `None` to skip.

Example interceptor that injects auth headers from LangGraph metadata:

```python
def build_auth_interceptor():
    async def interceptor(request, handler):
        from langgraph.config import get_config
        metadata = get_config().get("metadata", {})
        headers = dict(request.headers or {})
        if token := metadata.get("auth_token"):
            headers["X-Auth-Token"] = token
        return await handler(request.override(headers=headers))
    return interceptor
```

- A single string value is accepted and normalized to a one-element list.
- Invalid paths or builder failures are logged as warnings without blocking other interceptors.
- The builder return value must be `callable`; non-callable values are skipped with a warning.

## How It Works

MCP servers expose tools that are automatically discovered and integrated into DeerFlow’s agent system at runtime. Once enabled, these tools become available to agents without additional code changes.

## Example Capabilities

MCP servers can provide access to:

- **File systems**
- **Databases** (e.g., PostgreSQL)
- **External APIs** (e.g., GitHub, Brave Search)
- **Browser automation** (e.g., Puppeteer)
- **Custom MCP server implementations**

## Learn More

For detailed documentation about the Model Context Protocol, visit:  
https://modelcontextprotocol.io