For Server Developers

Get started building your own server to use in Claude for Desktop and other clients.

In this tutorial, we’ll build a simple MCP weather server and connect it to a host, Claude for Desktop. We’ll start with a basic setup, and then progress to more complex use cases.

What we’ll be building

Many LLMs (including Claude) do not currently have the ability to fetch the forecast and severe weather alerts. Let’s use MCP to solve that!

We’ll build a server that exposes two tools: get-alerts and get-forecast. Then we’ll connect the server to an MCP host (in this case, Claude for Desktop):

Servers can connect to any client. We’ve chosen Claude for Desktop here for simplicity, but we also have guides on building your own client as well as a list of other clients here.

Why Claude for Desktop and not Claude.ai?

Core MCP Concepts

MCP servers can provide three main types of capabilities:

Resources: File-like data that can be read by clients (like API responses or file contents)

Tools: Functions that can be called by the LLM (with user approval)

Prompts: Pre-written templates that help users accomplish specific tasks

This tutorial will primarily focus on tools.

Python

Let’s get started with building our weather server! You can find the complete code for what we’ll be building here.

Prerequisite knowledge

This quickstart assumes you have familiarity with:

Python

LLMs like Claude

System requirements

Python 3.10 or higher installed.

You must use the Python MCP SDK 1.2.0 or higher.

Set up your environment

First, let’s install uv and set up our Python project and environment:

MacOS/Linux

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

Windows

powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"

Make sure to restart your terminal afterwards to ensure that the uv command gets picked up.

Now, let’s create and set up our project:

MacOS/Linux

# Create a new directory for our project
uv init weather
cd weather

# Create virtual environment and activate it
uv venv
.venv\Scripts\activate

# Install dependencies
uv add mcp[cli] httpx

# Create our server file
new-item weather.py

Windows

# Create a new directory for our project
uv init weather
cd weather

# Create virtual environment and activate it
uv venv
.venv\Scripts\activate

# Install dependencies
uv add mcp[cli] httpx

# Create our server file
new-item weather.py

Now let’s dive into building your server.

Building your server

Importing packages and setting up the instance

Add these to the top of your weather.py:

The FastMCP class uses Python type hints and docstrings to automatically generate tool definitions, making it easy to create and maintain MCP tools.

Helper functions

Next, let’s add our helper functions for querying and formatting the data from the National Weather Service API:

Implementing tool execution

The tool execution handler is responsible for actually executing the logic of each tool. Let’s add it:

Running the server

Finally, let’s initialize and run the server:

Your server is complete! Run uv run weather.py to confirm that everything’s working.

Let’s now test your server from an existing MCP host, Claude for Desktop.

Testing your server with Claude for Desktop

Claude for Desktop is not yet available on Linux. Linux users can proceed to the Building a client tutorial to build an MCP client that connects to the server we just built.

First, make sure you have Claude for Desktop installed. You can install the latest version here. If you already have Claude for Desktop, make sure it’s updated to the latest version.

We’ll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at ~/Library/Application Support/Claude/claude_desktop_config.json in a text editor. Make sure to create the file if it doesn’t exist.

For example, if you have VS Code installed:

MacOS/Linux

Windows

code $env:AppData\Claude\claude_desktop_config.json

You’ll then add your servers in the mcpServers key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.

In this case, we’ll add our single weather server like so:

MacOS/Linux

{
    "mcpServers": {
        "weather": {
            "command": "uv",
            "args": [
                "--directory",
                "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather",
                "run",
                "weather.py"
            ]
        }
    }
}

Windows

{
    "mcpServers": {
        "weather": {
            "command": "uv",
            "args": [
                "--directory",
                "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather",
                "run",
                "weather.py"
            ]
        }
    }
}

You may need to put the full path to the uv executable in the command field. You can get this by running which uv on MacOS/Linux or where uv on Windows.

Make sure you pass in the absolute path to your server.

This tells Claude for Desktop:

There’s an MCP server named “weather”

To launch it by running uv --directory /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather run weather.py

Save the file, and restart Claude for Desktop.

Test with commands

Let’s make sure Claude for Desktop is picking up the two tools we’ve exposed in our weather server. You can do this by looking for the hammer

icon:

After clicking on the hammer icon, you should see two tools listed:

If your server isn’t being picked up by Claude for Desktop, proceed to the Troubleshooting section for debugging tips.

If the hammer icon has shown up, you can now test your server by running the following commands in Claude for Desktop:

What’s the weather in Sacramento?

What are the active weather alerts in Texas?

Since this is the US National Weather service, the queries will only work for US locations.

What’s happening under the hood

When you ask a question:

The client sends your question to Claude

Claude analyzes the available tools and decides which one(s) to use

The client executes the chosen tool(s) through the MCP server

The results are sent back to Claude

Claude formulates a natural language response

The response is displayed to you!

What we’ll be building#

Core MCP Concepts#

Prerequisite knowledge#

System requirements#

Set up your environment#

Building your server#

Importing packages and setting up the instance#

Helper functions#

Implementing tool execution#

Running the server#

Testing your server with Claude for Desktop#

Test with commands#

What’s happening under the hood#

What we’ll be building

Core MCP Concepts

Prerequisite knowledge

System requirements

Set up your environment

Building your server

Importing packages and setting up the instance

Helper functions

Implementing tool execution

Running the server

Testing your server with Claude for Desktop

Test with commands

What’s happening under the hood