fastmcp/docs/deployment/running-server.mdx

---
title: Running Your FastMCP Server
sidebarTitle: Running the Server
description: Learn how to run and deploy your FastMCP server using various transport protocols like STDIO, Streamable HTTP, and SSE.
icon: circle-play
---
import { VersionBadge } from '/snippets/version-badge.mdx'


FastMCP servers can be run in different ways depending on your application's needs, from local command-line tools to persistent web services. This guide covers the primary methods for running your server, focusing on the available transport protocols: STDIO, Streamable HTTP, and SSE.

## The `run()` Method

FastMCP servers can be run directly from Python by calling the `run()` method on a `FastMCP` instance.

<Tip>
For maximum compatibility, it's best practice to place the `run()` call within an `if __name__ == "__main__":` block. This ensures the server starts only when the script is executed directly, not when imported as a module.
</Tip>

```python {9-10} my_server.py
from fastmcp import FastMCP

mcp = FastMCP(name="MyServer")

@mcp.tool
def hello(name: str) -> str:
    return f"Hello, {name}!"

if __name__ == "__main__":
    mcp.run()
```
You can now run this MCP server by executing `python my_server.py`.

MCP servers can be run with a variety of different transport options, depending on your application's requirements. The `run()` method can take a `transport` argument and other transport-specific keyword arguments to configure how the server operates.

## The FastMCP CLI

FastMCP also provides a command-line interface for running servers without modifying the source code. After installing FastMCP, you can run your server directly from the command line:

```bash
fastmcp run server.py
```

<Tip>
**Important**: When using `fastmcp run`, it **ignores** the `if __name__ == "__main__"` block entirely. Instead, it looks for a FastMCP object named `mcp`, `server`, or `app` and calls its `run()` method directly with the transport options you specify.

This means you can use `fastmcp run` to override the transport specified in your code, which is particularly useful for testing or changing deployment methods without modifying the code.
</Tip>

You can specify transport options and other configuration:

```bash
fastmcp run server.py --transport sse --port 9000
```

For development and testing, you can use the `dev` command to run your server with the MCP Inspector:

```bash
fastmcp dev server.py
```

See the [CLI documentation](/patterns/cli) for detailed information about all available commands and options.

### Passing Arguments to Servers

When servers accept command line arguments (using argparse, click, or other libraries), you can pass them after `--`:

```bash
fastmcp run config_server.py -- --config config.json
fastmcp run database_server.py -- --database-path /tmp/db.sqlite --debug
```

This is useful for servers that need configuration files, database paths, API keys, or other runtime options.

## Transport Options

Below is a comparison of available transport options to help you choose the right one for your needs:

| Transport | Use Cases | Recommendation |
| --------- | --------- | -------------- |
| **STDIO** | Local tools, command-line scripts, and integrations with clients like Claude Desktop | Best for local tools and when clients manage server processes |
| **Streamable HTTP** | Web-based deployments, microservices, exposing MCP over a network | Recommended choice for web-based deployments |
| **SSE** | Existing web-based deployments that rely on SSE | Deprecated - prefer Streamable HTTP for new projects |

### STDIO

The STDIO transport is the default and most widely compatible option for local MCP server execution. It is ideal for local tools, command-line integrations, and clients like Claude Desktop. However, it has the disadvantage of having to run the MCP code locally, which can introduce security concerns with third-party servers.

STDIO is the default transport, so you don't need to specify it when calling `run()`. However, you can specify it explicitly to make your intent clear:

```python {6}
from fastmcp import FastMCP

mcp = FastMCP()

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

When using Stdio transport, you will typically *not* run the server yourself as a separate process. Rather, your *clients* will spin up a new server process for each session. As such, no additional configuration is required.

### Streamable HTTP

<VersionBadge version="2.3.0" />

Streamable HTTP is a modern, efficient transport for exposing your MCP server via HTTP. It is the recommended transport for web-based deployments.

To run a server using Streamable HTTP, you can use the `run()` method with the `transport` argument set to `"streamable-http"`. This will start a Uvicorn server on the default host (`127.0.0.1`), port (`8000`), and path (`/mcp`).
<CodeGroup>
```python {6} server.py
from fastmcp import FastMCP

mcp = FastMCP()

if __name__ == "__main__":
    mcp.run(transport="streamable-http")
```
```python {5} client.py
import asyncio
from fastmcp import Client

async def example():
    async with Client("http://127.0.0.1:8000/mcp") as client:
        await client.ping()

if __name__ == "__main__":
    asyncio.run(example())
```
</CodeGroup>

To customize the host, port, path, or log level, provide appropriate keyword arguments to the `run()` method.

<CodeGroup>
```python {8-11} server.py
from fastmcp import FastMCP

mcp = FastMCP()

if __name__ == "__main__":
    mcp.run(
        transport="streamable-http",
        host="127.0.0.1",
        port=4200,
        path="/my-custom-path",
        log_level="debug",
    )
```
```python {5} client.py
import asyncio
from fastmcp import Client

async def example():
    async with Client("http://127.0.0.1:4200/my-custom-path") as client:
        await client.ping()

if __name__ == "__main__":
    asyncio.run(example())
```
</CodeGroup>


### SSE

<Warning>
The SSE transport is deprecated and may be removed in a future version.
New applications should use Streamable HTTP transport instead.
</Warning>

Server-Sent Events (SSE) is an HTTP-based protocol for server-to-client streaming. While FastMCP still supports SSE, it is deprecated and Streamable HTTP is preferred for new projects.

To run a server using SSE, you can use the `run()` method with the `transport` argument set to `"sse"`. This will start a Uvicorn server on the default host (`127.0.0.1`), port (`8000`), and with default SSE path (`/sse`) and message path (`/messages/`).

<CodeGroup>
```python {6} server.py
from fastmcp import FastMCP

mcp = FastMCP()

if __name__ == "__main__":
    mcp.run(transport="sse")
```
```python {3,7} client.py
import asyncio
from fastmcp import Client
from fastmcp.client.transports import SSETransport

async def example():
    async with Client(
        transport=SSETransport("http://127.0.0.1:8000/sse")
    ) as client:
        await client.ping()

if __name__ == "__main__":
    asyncio.run(example())
```
</CodeGroup>

<Tip>
Notice that the client in the above example uses an explicit `SSETransport` to connect to the server. FastMCP will attempt to infer the appropriate transport from the provided configuration, but HTTP URLs are assumed to be Streamable HTTP (as of FastMCP 2.3.0).
</Tip>

To customize the host, port, or log level, provide appropriate keyword arguments to the `run()` method. You can also adjust the SSE path (which clients should connect to) and the message POST endpoint (which clients use to send subsequent messages).

<CodeGroup>
```python {8-12} server.py
from fastmcp import FastMCP

mcp = FastMCP()

if __name__ == "__main__":
    mcp.run(
        transport="sse",
        host="127.0.0.1",
        port=4200,
        log_level="debug",
        path="/my-custom-sse-path",
    )
```
```python {7} client.py
import asyncio
from fastmcp import Client
from fastmcp.client.transports import SSETransport

async def example():
    async with Client(
        transport=SSETransport("http://127.0.0.1:4200/my-custom-sse-path")
    ) as client:
        await client.ping()

if __name__ == "__main__":
    asyncio.run(example())
```
</CodeGroup>



## Async Usage

FastMCP provides both synchronous and asynchronous APIs for running your server. The `run()` method seen in previous examples is a synchronous method that internally uses `anyio.run()` to run the asynchronous server. For applications that are already running in an async context, FastMCP provides the `run_async()` method.

```python {10-12}
from fastmcp import FastMCP
import asyncio

mcp = FastMCP(name="MyServer")

@mcp.tool
def hello(name: str) -> str:
    return f"Hello, {name}!"

async def main():
    # Use run_async() in async contexts
    await mcp.run_async(transport="streamable-http")

if __name__ == "__main__":
    asyncio.run(main())
```

<Warning>
The `run()` method cannot be called from inside an async function because it already creates its own async event loop internally. If you attempt to call `run()` from inside an async function, you'll get an error about the event loop already running.

Always use `run_async()` inside async functions and `run()` in synchronous contexts.
</Warning>

Both `run()` and `run_async()` accept the same transport arguments, so all the examples above apply to both methods.

## Custom Routes

You can also add custom web routes to your FastMCP server, which will be exposed alongside the MCP endpoint. To do so, use the `@custom_route` decorator. Note that this is less flexible than using a full ASGI framework, but can be useful for adding simple endpoints like health checks to your standalone server.

```python
from fastmcp import FastMCP
from starlette.requests import Request
from starlette.responses import PlainTextResponse

mcp = FastMCP("MyServer")

@mcp.custom_route("/health", methods=["GET"])
async def health_check(request: Request) -> PlainTextResponse:
    return PlainTextResponse("OK")

if __name__ == "__main__":
    mcp.run()
```