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MCP Weather Server

by dfrho
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TypeScript
Remote

MCP WEATHER SERVER WRITTEN IN TYPESCRIPT

Protocol Map

This weather MCP server implements the Model Context Protocol (MCP) to provide weather data through a standardized interface. Below is the complete protocol mapping showing how the server communicates with MCP clients.

Server Information

Capabilities

{ "capabilities": { "tools": { "listChanged": true } } }

Tools

The server exposes two tools for weather data retrieval:

1. get_alerts

Retrieves active weather alerts for a US state.

Input Schema:

{ "type": "object", "properties": { "state": { "type": "string", "description": "Two-letter US state code (e.g. CA, NY)", "minLength": 2, "maxLength": 2 } }, "required": ["state"] }

Example Request:

{ "method": "tools/call", "params": { "name": "get_alerts", "arguments": { "state": "CA" } } }

Example Response:

{ "content": [ { "type": "text", "text": "Event: Heat Advisory\nArea: Los Angeles County\nSeverity: Moderate\nDescription: Dangerously hot conditions...\nInstructions: Drink plenty of fluids..." } ] }

Error Response:

{ "content": [ { "type": "text", "text": "Unable to fetch alerts or no alerts found." } ] }

2. get_forecast

Retrieves weather forecast for a specific location using latitude and longitude coordinates.

Input Schema:

{ "type": "object", "properties": { "latitude": { "type": "number", "description": "Latitude of the location", "minimum": -90, "maximum": 90 }, "longitude": { "type": "number", "description": "Longitude of the location", "minimum": -180, "maximum": 180 } }, "required": ["latitude", "longitude"] }

Example Request:

{ "method": "tools/call", "params": { "name": "get_forecast", "arguments": { "latitude": 38.5816, "longitude": -121.4944 } } }

Example Response:

{ "content": [ { "type": "text", "text": "Tonight:\nTemperature: 65°F\nWind: 5 mph SW\nForecast: Partly cloudy with a slight chance of showers.\n---\nTomorrow:\nTemperature: 78°F\nWind: 10 mph W\nForecast: Sunny skies throughout the day." } ] }

Error Responses:

{ "content": [ { "type": "text", "text": "Failed to retrieve grid point data for coordinates: 38.5816, -121.4944. This location may not be supported by the NWS API (only US locations are supported)." } ] }

Communication Flow

sequenceDiagram participant Client as MCP Client (Claude) participant Server as Weather Server participant NWS as National Weather Service API Client->>Server: Initialize Connection (STDIO) Server->>Client: Server Info + Capabilities Client->>Server: List Tools Server->>Client: [get_alerts, get_forecast] Client->>Server: Call Tool: get_forecast(lat, lon) Server->>NWS: GET /points/{lat},{lon} NWS->>Server: Grid Point Data Server->>NWS: GET {forecast_url} NWS->>Server: Forecast Data Server->>Client: Formatted Forecast Text Client->>Server: Call Tool: get_alerts(state) Server->>NWS: GET /alerts/active/area/{state} NWS->>Server: Active Alerts Server->>Client: Formatted Alerts Text

Protocol Messages

Initialization

Client → Server:

{ "jsonrpc": "2.0", "id": 1, "method": "initialize", "params": { "protocolVersion": "2024-11-05", "capabilities": {}, "clientInfo": { "name": "Claude Desktop", "version": "1.0.0" } } }

Server → Client:

{ "jsonrpc": "2.0", "id": 1, "result": { "protocolVersion": "2024-11-05", "capabilities": { "tools": { "listChanged": true } }, "serverInfo": { "name": "weather", "version": "1.0.0" } } }

Tool Discovery

Client → Server:

{ "jsonrpc": "2.0", "id": 2, "method": "tools/list" }

Server → Client:

{ "jsonrpc": "2.0", "id": 2, "result": { "tools": [ { "name": "get_alerts", "description": "Get weather alerts for a US state.", "inputSchema": { "type": "object", "properties": { "state": { "type": "string", "description": "Two-letter US 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"] } } ] } }

External API Integration

National Weather Service API

The server integrates with the following NWS API endpoints:

Endpoint

Purpose

Rate Limit

GET /alerts/active/area/{state}

Retrieve active alerts for a state

User-Agent required

GET /points/{latitude},{longitude}

Get grid point metadata

User-Agent required

GET {forecast_url}

Retrieve detailed forecast

User-Agent required

Required Headers:

User-Agent: weather-app/1.0 Accept: application/geo+json

Error Handling

The server implements graceful error handling for:

  1. Invalid coordinates: Returns error message for non-US locations

  2. Network failures: Returns "Unable to fetch..." messages

  3. Missing data: Returns "No active alerts" or similar user-friendly messages

  4. API errors: Catches and handles HTTP errors from NWS API

Transport Layer

  • Type: STDIO (Standard Input/Output)

  • Encoding: UTF-8

  • Message Format: JSON-RPC 2.0

  • Framing: Newline-delimited JSON

Security Considerations

  1. Input Validation: All parameters are validated against schema

  2. Rate Limiting: Respects NWS API rate limits

  3. Error Sanitization: External API errors are sanitized before returning to client

  4. No Authentication: Server uses public NWS API (no credentials required)

Logging

  • STDIO Servers: All logs written to stderr (never stdout)

  • Log Location: Configured in MCP client (e.g., ~/Library/Logs/Claude/mcp-server-weather.log)

  • Log Level: Errors and warnings only (to avoid STDIO corruption)

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