title	description
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](/quickstart/client) as well as a [list of other clients here](/clients). Because servers are locally run, MCP currently only supports desktop hosts. Remote hosts are in active development.

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.

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:

curl -LsSf https://astral.sh/uv/install.sh | sh

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:

```bash MacOS/Linux # Create a new directory for our project uv init weather cd weather

Create virtual environment and activate it

uv venv source .venv/bin/activate

Install dependencies

uv add mcp[cli] httpx

Create our server file

touch weather.py


```powershell 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:

from typing import Any
import httpx
from mcp.server.fastmcp import FastMCP

# Initialize FastMCP server
mcp = FastMCP("weather")

# Constants
NWS_API_BASE = "https://api.weather.gov"
USER_AGENT = "weather-app/1.0"

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:

async def make_nws_request(url: str) -> dict[str, Any] | None:
    """Make a request to the NWS API with proper error handling."""
    headers = {
        "User-Agent": USER_AGENT,
        "Accept": "application/geo+json"
    }
    async with httpx.AsyncClient() as client:
        try:
            response = await client.get(url, headers=headers, timeout=30.0)
            response.raise_for_status()
            return response.json()
        except Exception:
            return None

def format_alert(feature: dict) -> str:
    """Format an alert feature into a readable string."""
    props = feature["properties"]
    return f"""
Event: {props.get('event', 'Unknown')}
Area: {props.get('areaDesc', 'Unknown')}
Severity: {props.get('severity', 'Unknown')}
Description: {props.get('description', 'No description available')}
Instructions: {props.get('instruction', 'No specific instructions provided')}
"""

Implementing tool execution

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

@mcp.tool()
async def get_alerts(state: str) -> str:
    """Get weather alerts for a US state.

    Args:
        state: Two-letter US state code (e.g. CA, NY)
    """
    url = f"{NWS_API_BASE}/alerts/active/area/{state}"
    data = await make_nws_request(url)

    if not data or "features" not in data:
        return "Unable to fetch alerts or no alerts found."

    if not data["features"]:
        return "No active alerts for this state."

    alerts = [format_alert(feature) for feature in data["features"]]
    return "\n---\n".join(alerts)

@mcp.tool()
async def get_forecast(latitude: float, longitude: float) -> str:
    """Get weather forecast for a location.

    Args:
        latitude: Latitude of the location
        longitude: Longitude of the location
    """
    # First get the forecast grid endpoint
    points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
    points_data = await make_nws_request(points_url)

    if not points_data:
        return "Unable to fetch forecast data for this location."

    # Get the forecast URL from the points response
    forecast_url = points_data["properties"]["forecast"]
    forecast_data = await make_nws_request(forecast_url)

    if not forecast_data:
        return "Unable to fetch detailed forecast."

    # Format the periods into a readable forecast
    periods = forecast_data["properties"]["periods"]
    forecasts = []
    for period in periods[:5]:  # Only show next 5 periods
        forecast = f"""
{period['name']}:
Temperature: {period['temperature']}°{period['temperatureUnit']}
Wind: {period['windSpeed']} {period['windDirection']}
Forecast: {period['detailedForecast']}
"""
        forecasts.append(forecast)

    return "\n---\n".join(forecasts)

Running the server

Finally, let's initialize and run the server:

if __name__ == "__main__":
    # Initialize and run the server
    mcp.run(transport='stdio')

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](/quickstart/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:

```bash code ~/Library/Application\ Support/Claude/claude_desktop_config.json ``` ```powershell 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:

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

Save the file, and restart Claude for Desktop.

Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript)

Prerequisite knowledge

This quickstart assumes you have familiarity with:

TypeScript
LLMs like Claude

System requirements

For TypeScript, make sure you have the latest version of Node installed.

Set up your environment

First, let's install Node.js and npm if you haven't already. You can download them from nodejs.org. Verify your Node.js installation:

node --version
npm --version

For this tutorial, you'll need Node.js version 16 or higher.

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

```bash MacOS/Linux # Create a new directory for our project mkdir weather cd weather

Initialize a new npm project

npm init -y

Install dependencies

npm install @modelcontextprotocol/sdk zod npm install -D @types/node typescript

Create our files

mkdir src touch src/index.ts


```powershell Windows
# Create a new directory for our project
md weather
cd weather

# Initialize a new npm project
npm init -y

# Install dependencies
npm install @modelcontextprotocol/sdk zod
npm install -D @types/node typescript

# Create our files
md src
new-item src\index.ts

Update your package.json to add type: "module" and a build script:

{
  "type": "module",
  "bin": {
    "weather": "./build/index.js"
  },
  "scripts": {
    "build": "tsc && node -e \"require('fs').chmodSync('build/index.js', '755')\"",
  },
  "files": [
    "build"
  ],
}

Create a tsconfig.json in the root of your project:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "Node16",
    "moduleResolution": "Node16",
    "outDir": "./build",
    "rootDir": "./src",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Now let's dive into building your server.

Building your server

Importing packages

Add these to the top of your src/index.ts:

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod";

Setting up the instance

Then initialize the NWS API base URL, validation schemas, and server instance:

const NWS_API_BASE = "https://api.weather.gov";
const USER_AGENT = "weather-app/1.0";

// Define Zod schemas for validation
const AlertsArgumentsSchema = z.object({
  state: z.string().length(2),
});

const ForecastArgumentsSchema = z.object({
  latitude: z.number().min(-90).max(90),
  longitude: z.number().min(-180).max(180),
});

// Create server instance
const server = new Server(
  {
    name: "weather",
    version: "1.0.0",
  },
  {
    capabilities: {
      tools: {},
    },
  }
);

Implementing tool listing

We need to tell clients what tools are available. This server.setRequestHandler call will register this list for us:

// List available tools
server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [
      {
        name: "get-alerts",
        description: "Get weather alerts for a state",
        inputSchema: {
          type: "object",
          properties: {
            state: {
              type: "string",
              description: "Two-letter state code (e.g. CA, NY)",
            },
          },
          required: ["state"],
        },
      },
      {
        name: "get-forecast",
        description: "Get weather forecast for a location",
        inputSchema: {
          type: "object",
          properties: {
            latitude: {
              type: "number",
              description: "Latitude of the location",
            },
            longitude: {
              type: "number",
              description: "Longitude of the location",
            },
          },
          required: ["latitude", "longitude"],
        },
      },
    ],
  };
});

This defines our two tools: get-alerts and get-forecast.

Helper functions

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

// Helper function for making NWS API requests
async function makeNWSRequest<T>(url: string): Promise<T | null> {
  const headers = {
    "User-Agent": USER_AGENT,
    Accept: "application/geo+json",
  };

  try {
    const response = await fetch(url, { headers });
    if (!response.ok) {
      throw new Error(`HTTP error! status: ${response.status}`);
    }
    return (await response.json()) as T;
  } catch (error) {
    console.error("Error making NWS request:", error);
    return null;
  }
}

interface AlertFeature {
  properties: {
    event?: string;
    areaDesc?: string;
    severity?: string;
    status?: string;
    headline?: string;
  };
}

// Format alert data
function formatAlert(feature: AlertFeature): string {
  const props = feature.properties;
  return [
    `Event: ${props.event || "Unknown"}`,
    `Area: ${props.areaDesc || "Unknown"}`,
    `Severity: ${props.severity || "Unknown"}`,
    `Status: ${props.status || "Unknown"}`,
    `Headline: ${props.headline || "No headline"}`,
    "---",
  ].join("\n");
}

interface ForecastPeriod {
  name?: string;
  temperature?: number;
  temperatureUnit?: string;
  windSpeed?: string;
  windDirection?: string;
  shortForecast?: string;
}

interface AlertsResponse {
  features: AlertFeature[];
}

interface PointsResponse {
  properties: {
    forecast?: string;
  };
}

interface ForecastResponse {
  properties: {
    periods: ForecastPeriod[];
  };
}

Implementing tool execution

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

// Handle tool execution
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  const { name, arguments: args } = request.params;

  try {
    if (name === "get-alerts") {
      const { state } = AlertsArgumentsSchema.parse(args);
      const stateCode = state.toUpperCase();

      const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
      const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);

      if (!alertsData) {
        return {
          content: [
            {
              type: "text",
              text: "Failed to retrieve alerts data",
            },
          ],
        };
      }

      const features = alertsData.features || [];
      if (features.length === 0) {
        return {
          content: [
            {
              type: "text",
              text: `No active alerts for ${stateCode}`,
            },
          ],
        };
      }

      const formattedAlerts = features.map(formatAlert).slice(0, 20) // only take the first 20 alerts;
      const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join(
        "\n"
      )}`;

      return {
        content: [
          {
            type: "text",
            text: alertsText,
          },
        ],
      };
    } else if (name === "get-forecast") {
      const { latitude, longitude } = ForecastArgumentsSchema.parse(args);

      // Get grid point data
      const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(
        4
      )},${longitude.toFixed(4)}`;
      const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);

      if (!pointsData) {
        return {
          content: [
            {
              type: "text",
              text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
            },
          ],
        };
      }

      const forecastUrl = pointsData.properties?.forecast;
      if (!forecastUrl) {
        return {
          content: [
            {
              type: "text",
              text: "Failed to get forecast URL from grid point data",
            },
          ],
        };
      }

      // Get forecast data
      const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
      if (!forecastData) {
        return {
          content: [
            {
              type: "text",
              text: "Failed to retrieve forecast data",
            },
          ],
        };
      }

      const periods = forecastData.properties?.periods || [];
      if (periods.length === 0) {
        return {
          content: [
            {
              type: "text",
              text: "No forecast periods available",
            },
          ],
        };
      }

      // Format forecast periods
      const formattedForecast = periods.map((period: ForecastPeriod) =>
        [
          `${period.name || "Unknown"}:`,
          `Temperature: ${period.temperature || "Unknown"}°${
            period.temperatureUnit || "F"
          }`,
          `Wind: ${period.windSpeed || "Unknown"} ${
            period.windDirection || ""
          }`,
          `${period.shortForecast || "No forecast available"}`,
          "---",
        ].join("\n")
      );

      const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join(
        "\n"
      )}`;

      return {
        content: [
          {
            type: "text",
            text: forecastText,
          },
        ],
      };
    } else {
      throw new Error(`Unknown tool: ${name}`);
    }
  } catch (error) {
    if (error instanceof z.ZodError) {
      throw new Error(
        `Invalid arguments: ${error.errors
          .map((e) => `${e.path.join(".")}: ${e.message}`)
          .join(", ")}`
      );
    }
    throw error;
  }
});

Running the server

Finally, implement the main function to run the server:

// Start the server
async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
  console.error("Weather MCP Server running on stdio");
}

main().catch((error) => {
  console.error("Fatal error in main():", error);
  process.exit(1);
});

Make sure to run npm run build to build your server! This is a very important step in getting your server to connect.

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](/quickstart/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:

```bash code ~/Library/Application\ Support/Claude/claude_desktop_config.json ``` ```powershell 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:

```json Node { "mcpServers": { "weather": { "command": "node", "args": [ "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js" ] } } } ``` ```json Node { "mcpServers": { "weather": { "command": "node", "args": [ "C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\index.js" ] } } } ```

This tells Claude for Desktop:

There's an MCP server named "weather"
Launch it by running node /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js

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 <img src="/images/claude-desktop-mcp-hammer-icon.svg" style={{display: 'inline', margin: 0, height: '1.3em'}} /> 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!

Troubleshooting

**Getting logs from Claude for Desktop**

Claude.app logging related to MCP is written to log files in ~/Library/Logs/Claude:

mcp.log will contain general logging about MCP connections and connection failures.
Files named mcp-server-SERVERNAME.log will contain error (stderr) logging from the named server.

You can run the following command to list recent logs and follow along with any new ones:

# Check Claude's logs for errors
tail -n 20 -f ~/Library/Logs/Claude/mcp*.log

Server not showing up in Claude

Check your claude_desktop_config.json file syntax
Make sure the path to your project is absolute and not relative
Restart Claude for Desktop completely

Tool calls failing silently

If Claude attempts to use the tools but they fail:

Check Claude's logs for errors
Verify your server builds and runs without errors
Try restarting Claude for Desktop

None of this is working. What do I do?

Please refer to our debugging guide for better debugging tools and more detailed guidance. Error: Failed to retrieve grid point data

This usually means either:

The coordinates are outside the US
The NWS API is having issues
You're being rate limited

Fix:

Verify you're using US coordinates
Add a small delay between requests
Check the NWS API status page

Error: No active alerts for [STATE]

This isn't an error - it just means there are no current weather alerts for that state. Try a different state or check during severe weather.

For more advanced troubleshooting, check out our guide on [Debugging MCP](/docs/tools/debugging)

Next steps

Learn how to build your own MCP client that can connect to your server Check out our gallery of official MCP servers and implementations Learn how to effectively debug MCP servers and integrations Learn how to use LLMs like Claude to speed up your MCP development

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Files

server.mdx

server.mdx

What we'll be building

Core MCP Concepts

Prerequisite knowledge

System requirements

Set up your environment

Create virtual environment and activate it

Install dependencies

Create our server file

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

Prerequisite knowledge

System requirements

Set up your environment

Initialize a new npm project

Install dependencies

Create our files

Building your server

Importing packages

Setting up the instance

Implementing tool listing

Helper functions

Implementing tool execution

Running the server

Testing your server with Claude for Desktop

Test with commands

What's happening under the hood

Troubleshooting

Next steps

Files

server.mdx

Latest commit

History

server.mdx

File metadata and controls

What we'll be building

Core MCP Concepts

Prerequisite knowledge

System requirements

Set up your environment

Create virtual environment and activate it

Install dependencies

Create our server file

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

Prerequisite knowledge

System requirements

Set up your environment

Initialize a new npm project

Install dependencies

Create our files

Building your server

Importing packages

Setting up the instance

Implementing tool listing

Helper functions

Implementing tool execution

Running the server

Testing your server with Claude for Desktop

Test with commands

What's happening under the hood

Troubleshooting

Next steps