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

# Custom MCP Server

## Overview

Use Google ADK `McpToolset` to connect to an MCP server and register it with `Agent(tools=[toolset])`. The older `MCPToolset` name remains compatible. Remote servers require a supported MCP URL and credentials; local servers require an executable command and its dependencies.

## Usage

Set `MCP_SERVER_URL` and `MCP_SERVER_TOKEN`, then verify tool discovery below. Discovery requires no reasoning model; complete [model configuration](/productions/veadk/preview/en/components/agent/model) before invoking tools through an agent.

```python title="mcp_connection.py" lines theme={null}
import asyncio
import os
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset
from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams

async def main():
    toolset = McpToolset(
        connection_params=StreamableHTTPConnectionParams(
            url=os.environ["MCP_SERVER_URL"],
            headers={"Authorization": f"Bearer {os.environ['MCP_SERVER_TOKEN']}"},
        ),
    )
    try:
        print([tool.name for tool in await toolset.get_tools()])
    finally:
        await toolset.close()

asyncio.run(main())
```

### Local standard input/output connection

Save these files in the same directory, install `python -m pip install "mcp[cli]"`, and run `python check_local_mcp.py`. The output should include `add`. The client starts the server and closes it when the example ends.

```python title="local_mcp_server.py" lines theme={null}
from mcp.server.fastmcp import FastMCP

server = FastMCP("calculator")

@server.tool()
def add(a: float, b: float) -> float:
    """Add two numbers."""
    return a + b

if __name__ == "__main__":
    server.run(transport="stdio")
```

```python title="check_local_mcp.py" lines theme={null}
import asyncio
import sys
from pathlib import Path
from mcp import StdioServerParameters
from google.adk.tools.mcp_tool.mcp_toolset import McpToolset
from google.adk.tools.mcp_tool.mcp_session_manager import StdioConnectionParams

async def main():
    toolset = McpToolset(connection_params=StdioConnectionParams(
        server_params=StdioServerParameters(
            command=sys.executable,
            args=[str(Path(__file__).with_name("local_mcp_server.py"))],
        ),
        timeout=10.0,
    ))
    try:
        print([tool.name for tool in await toolset.get_tools()])
    finally:
        await toolset.close()

asyncio.run(main())
```

## Parameters

These constructor parameters correspond to Google ADK 2.2.0; other versions may support a different set.

| Parameter | Type | Default | Description |
| :- | :- | :- | :- |
| `connection_params` | `StdioConnectionParams \| StdioServerParameters \| SseConnectionParams \| StreamableHTTPConnectionParams` | `Required` | Transport and endpoint or local server command |
| `tool_filter` | `list[str] \| Callable` | `None` | Limit exposed tools; None exposes all |
| `tool_name_prefix` | `str \| None` | `None` | Prefix tool names to avoid collisions |
| `errlog` | `TextIO` | `sys.stderr` | Local server diagnostics |
| `auth_scheme` | `AuthScheme \| None` | `None` | Authentication scheme |
| `auth_credential` | `AuthCredential \| None` | `None` | Authentication credential |
| `require_confirmation` | `bool \| Callable` | `False` | Request confirmation before tool execution |
| `header_provider` | `Callable \| None` | `None` | Build request headers from the current context |
| `progress_callback` | `Callable \| None` | `None` | Receive server progress updates |
| `use_mcp_resources` | `bool` | `False` | Expose MCP resources |
| `sampling_callback` | `Callable \| None` | `None` | Handle server sampling requests |
| `sampling_capabilities` | `SamplingCapability \| None` | `None` | Advertised sampling capabilities |
| `credential_key` | `str \| None` | `None` | Key used to resolve credentials |

Streamable HTTP connections accept required `url`, `headers=None`, `timeout=5.0`, `sse_read_timeout=300.0`, and `terminate_on_close=True`. Timeouts are in seconds. `httpx_client_factory` defaults to the SDK HTTP client factory; override it only for a custom transport. Local connections use `StdioConnectionParams(server_params=..., timeout=5.0)`. Use `SseConnectionParams` for SSE servers; SSE and Streamable HTTP endpoints are not interchangeable.

## Automatic reconnection after session interruption

VeADK re-establishes disconnected MCP sessions and retries eligible tool discovery or calls once. A second failure returns an error, and cancellation does not trigger a retry. Services must still provide idempotency for tools that change external data: a connection retry does not guarantee exactly-once business execution.