--- title: "For Server Developers" description: "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: 1. **Resources**: File-like data that can be read by clients (like API responses or file contents) 2. **Tools**: Functions that can be called by the LLM (with user approval) 3. **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.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python) ### Prerequisite knowledge This quickstart assumes you have familiarity with: - Python - LLMs like Claude ### System requirements For Python, make sure you have Python 3.9 or higher installed. ### Set up your environment First, let's install `uv` and set up our Python project and environment: ```bash MacOS/Linux curl -LsSf https://astral.sh/uv/install.sh | sh ``` ```powershell 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: ```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 httpx # Remove template file rm hello.py # Create our files mkdir -p src/weather touch src/weather/__init__.py touch src/weather/server.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 httpx # Clean up boilerplate code rm hello.py # Create our files md src md src\weather new-item src\weather\__init__.py new-item src\weather\server.py ``` Add this code to `pyproject.toml`: ```toml ...rest of config [build-system] requires = [ "hatchling",] build-backend = "hatchling.build" [project.scripts] weather = "weather:main" ``` Add this code to `__init__.py`: ```python src/weather/__init__.py from . import server import asyncio def main(): """Main entry point for the package.""" asyncio.run(server.main()) # Optionally expose other important items at package level __all__ = ['main', 'server'] ``` Now let's dive into building your server. ## Building your server ### Importing packages Add these to the top of your `server.py`: ```python from typing import Any import asyncio import httpx from mcp.server.models import InitializationOptions import mcp.types as types from mcp.server import NotificationOptions, Server import mcp.server.stdio ``` ### Setting up the instance Then initialize the server instance and the base URL for the NWS API: ```python NWS_API_BASE = "https://api.weather.gov" USER_AGENT = "weather-app/1.0" server = Server("weather") ``` ### Implementing tool listing We need to tell clients what tools are available. The `list_tools()` decorator registers this handler: ```python @server.list_tools() async def handle_list_tools() -> list[types.Tool]: """ List available tools. Each tool specifies its arguments using JSON Schema validation. """ return [ types.Tool( 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"], }, ), types.Tool( 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: ```python async def make_nws_request(client: httpx.AsyncClient, 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" } 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 concise string.""" props = feature["properties"] return ( f"Event: {props.get('event', 'Unknown')}\n" f"Area: {props.get('areaDesc', 'Unknown')}\n" f"Severity: {props.get('severity', 'Unknown')}\n" f"Status: {props.get('status', 'Unknown')}\n" f"Headline: {props.get('headline', 'No headline')}\n" "---" ) ``` ### Implementing tool execution The tool execution handler is responsible for actually executing the logic of each tool. Let's add it: ```python @server.call_tool() async def handle_call_tool( name: str, arguments: dict | None ) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]: """ Handle tool execution requests. Tools can fetch weather data and notify clients of changes. """ if not arguments: raise ValueError("Missing arguments") if name == "get-alerts": state = arguments.get("state") if not state: raise ValueError("Missing state parameter") # Convert state to uppercase to ensure consistent format state = state.upper() if len(state) != 2: raise ValueError("State must be a two-letter code (e.g. CA, NY)") async with httpx.AsyncClient() as client: alerts_url = f"{NWS_API_BASE}/alerts?area={state}" alerts_data = await make_nws_request(client, alerts_url) if not alerts_data: return [types.TextContent(type="text", text="Failed to retrieve alerts data")] features = alerts_data.get("features", []) if not features: return [types.TextContent(type="text", text=f"No active alerts for {state}")] # Format each alert into a concise string formatted_alerts = [format_alert(feature) for feature in features[:20]] # only take the first 20 alerts alerts_text = f"Active alerts for {state}:\n\n" + "\n".join(formatted_alerts) return [ types.TextContent( type="text", text=alerts_text ) ] elif name == "get-forecast": try: latitude = float(arguments.get("latitude")) longitude = float(arguments.get("longitude")) except (TypeError, ValueError): return [types.TextContent( type="text", text="Invalid coordinates. Please provide valid numbers for latitude and longitude." )] # Basic coordinate validation if not (-90 <= latitude <= 90) or not (-180 <= longitude <= 180): return [types.TextContent( type="text", text="Invalid coordinates. Latitude must be between -90 and 90, longitude between -180 and 180." )] async with httpx.AsyncClient() as client: # First get the grid point lat_str = f"{latitude}" lon_str = f"{longitude}" points_url = f"{NWS_API_BASE}/points/{lat_str},{lon_str}" points_data = await make_nws_request(client, points_url) if not points_data: return [types.TextContent(type="text", text=f"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).")] # Extract forecast URL from the response properties = points_data.get("properties", {}) forecast_url = properties.get("forecast") if not forecast_url: return [types.TextContent(type="text", text="Failed to get forecast URL from grid point data")] # Get the forecast forecast_data = await make_nws_request(client, forecast_url) if not forecast_data: return [types.TextContent(type="text", text="Failed to retrieve forecast data")] # Format the forecast periods periods = forecast_data.get("properties", {}).get("periods", []) if not periods: return [types.TextContent(type="text", text="No forecast periods available")] # Format each period into a concise string formatted_forecast = [] for period in periods: forecast_text = ( f"{period.get('name', 'Unknown')}:\n" f"Temperature: {period.get('temperature', 'Unknown')}°{period.get('temperatureUnit', 'F')}\n" f"Wind: {period.get('windSpeed', 'Unknown')} {period.get('windDirection', '')}\n" f"{period.get('shortForecast', 'No forecast available')}\n" "---" ) formatted_forecast.append(forecast_text) forecast_text = f"Forecast for {latitude}, {longitude}:\n\n" + "\n".join(formatted_forecast) return [types.TextContent( type="text", text=forecast_text )] else: raise ValueError(f"Unknown tool: {name}") ``` ### Running the server Finally, implement the main function to run the server: ```python async def main(): # Run the server using stdin/stdout streams async with mcp.server.stdio.stdio_server() as (read_stream, write_stream): await server.run( read_stream, write_stream, InitializationOptions( server_name="weather", server_version="0.1.0", capabilities=server.get_capabilities( notification_options=NotificationOptions(), experimental_capabilities={}, ), ), ) # This is needed if you'd like to connect to a custom client if __name__ == "__main__": asyncio.run(main()) ``` Your server is complete! Run `uv run src/weather/server.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.](https://claude.ai/download) 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](https://code.visualstudio.com/) 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" ] } } } ``` ```json Python { "mcpServers": { "weather": { "command": "uv", "args": [ "--directory", "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather", "run", "weather" ] } } } ``` Make sure you pass in the absolute path to your server. This tells Claude for Desktop: 1. There's an MCP server named "weather" 2. 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](https://nodejs.org/). Verify your Node.js installation: ```bash 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: ```json package.json { "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: ```json tsconfig.json { "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`: ```typescript 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: ```typescript 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: ```typescript // 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: ```typescript // Helper function for making NWS API requests async function makeNWSRequest(url: string): Promise { 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: ${props.headline || "No headline"}`, "---", ].join("\n"); } interface ForecastPeriod { name?: string; temperature?: number; temperatureUnit?: string; windSpeed?: string; windDirection?: string; shortForecast?: string; } interface AlertsResponse { features: AlertFeature[]; } interface PointsResponse { properties: { forecast?: string; }; } interface ForecastResponse { properties: { periods: ForecastPeriod[]; }; } ``` ### Implementing tool execution The tool execution handler is responsible for actually executing the logic of each tool. Let's add it: ```typescript // Handle tool execution server.setRequestHandler(CallToolRequestSchema, async (request) => { const { name, arguments: args } = request.params; try { if (name === "get-alerts") { const { state } = AlertsArgumentsSchema.parse(args); const stateCode = state.toUpperCase(); const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`; const alertsData = await makeNWSRequest(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(pointsUrl); if (!pointsData) { return { content: [ { type: "text", text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`, }, ], }; } const forecastUrl = pointsData.properties?.forecast; if (!forecastUrl) { return { content: [ { type: "text", text: "Failed to get forecast URL from grid point data", }, ], }; } // Get forecast data const forecastData = await makeNWSRequest(forecastUrl); if (!forecastData) { return { content: [ { type: "text", text: "Failed to retrieve forecast data", }, ], }; } const periods = forecastData.properties?.periods || []; if (periods.length === 0) { return { content: [ { type: "text", text: "No forecast periods available", }, ], }; } // Format forecast periods const formattedForecast = periods.map((period: ForecastPeriod) => [ `${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: ```typescript // 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.](https://claude.ai/download) 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](https://code.visualstudio.com/) 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: 1. There's an MCP server named "weather" 2. 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 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](#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: 1. The client sends your question to Claude 2. Claude analyzes the available tools and decides which one(s) to use 3. The client executes the chosen tool(s) through the MCP server 4. The results are sent back to Claude 5. Claude formulates a natural language response 6. 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: ```bash # Check Claude's logs for errors tail -n 20 -f ~/Library/Logs/Claude/mcp*.log ``` **Server not showing up in Claude** 1. Check your `claude_desktop_config.json` file syntax 2. Make sure the path to your project is absolute and not relative 3. Restart Claude for Desktop completely **Tool calls failing silently** If Claude attempts to use the tools but they fail: 1. Check Claude's logs for errors 2. Verify your server builds and runs without errors 3. Try restarting Claude for Desktop **None of this is working. What do I do?** Please refer to our [debugging guide](/docs/tools/debugging) for better debugging tools and more detailed guidance. **Error: Failed to retrieve grid point data** This usually means either: 1. The coordinates are outside the US 2. The NWS API is having issues 3. 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