# Your First Server and Tool — Agent Frameworks and MCP Basics

Source: https://www.geekswithgeeks.com/en/agent-frameworks-mcp/srv-first-tool

> Create a server with the official Python SDK and expose a typed function as a tool.

## FastMCP in a few lines

The official Python SDK includes `FastMCP`. You create a server object and decorate normal functions with `@mcp.tool()`. The SDK builds the JSON schema from your type hints and uses the docstring as the description, so good types and docstrings are your tool documentation.

## From function to server

Decorate plain functions, choose a transport, run the server and test it with an inspector.

![Four steps: write, expose, run, inspect.](assets/figures/agent-frameworks-mcp/section-4-map.svg) — Figure 4.1 — Write, expose, run and inspect.

## A calculator server

Install with `pip install "mcp[cli]"`. The default transport is stdio, so the host starts this script as a subprocess.

```python
from mcp.server.fastmcp import FastMCP

mcp = FastMCP("calculator")

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two integers and return the sum."""
    return a + b

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

## Never print to stdout on stdio

With the stdio transport, standard output carries the protocol messages. A stray `print()` corrupts the stream. Log to standard error or a file instead.

**Quiz:** Where does FastMCP get a tool's input schema from?

- [x] From the function's type hints
- [ ] From a random guess
- [ ] From the filename
- [ ] From the operating system

*Answer:* From the function's type hints. Type hints define parameter types and the docstring becomes the description.