NASA MCP Server

Instructions

Implementation Reference

• src/handlers/jpl/horizons_file.ts:14-100 (handler)

  The core handler function `horizonsFileHandler` that executes the `jpl_horizons_file` tool. It formats input parameters into a Horizons-compatible text file, submits via multipart POST to the JPL API, processes the response, adds it as a resource, and returns formatted output.

  export async function horizonsFileHandler(args: Record<string, any>) {
    try {
      // Base URL for the Horizons File API (POST)
      const baseUrl = 'https://ssd.jpl.nasa.gov/api/horizons_file.api';
      
      // Format arguments into the key='value' text format for the input file
      // DO NOT include format here, it's a separate form field.
      const formattedArgs = { ...args };
      delete formattedArgs.format; // Remove format if present
  
      let fileContent = '!$$SOF\n'; // Add !SOF marker
      for (const [key, value] of Object.entries(formattedArgs)) {
        let formattedValue: string | number;
        const upperKey = key.toUpperCase();
  
        // Leave numbers unquoted
        if (typeof value === 'number') {
          formattedValue = value;
        } 
        // Quote ALL other values (strings, including YES/NO)
        else {
          formattedValue = `'${String(value).replace(/'/g, "\'")}'`;
        }
        
        fileContent += `${upperKey}=${formattedValue}\n`;
      }
      fileContent += '!$$EOF\n'; // Correct !EOF marker
  
      // Create FormData payload
      const form = new FormData();
      // Add format as a separate field
      form.append('format', args.format || 'json'); 
      // Add the file content under the 'input' field name
      form.append('input', fileContent, {
        filename: 'horizons_input.txt', // Required filename, content doesn't matter
        contentType: 'text/plain',
      });
  
      // Make the API request using POST with multipart/form-data
      const response = await axios.post(baseUrl, form, {
        headers: {
          ...form.getHeaders(), // Important for correct boundary
        },
      });
      const data = response.data; // Assume response is JSON based on 'format=json'
  
      // Create a resource URI that represents this query (similar to GET handler)
      let resourceUri = 'jpl://horizons-file'; // Distinguish from GET
      let resourceName = 'JPL Horizons file-based ephemeris data';
  
      if (args.COMMAND) {
        resourceUri += `/object/${encodeURIComponent(args.COMMAND)}`;
        resourceName = `${args.COMMAND} ephemeris data (file input)`;
        if (args.START_TIME && args.STOP_TIME) {
          resourceName += ` (${args.START_TIME} to ${args.STOP_TIME})`;
        }
      }
      
      // Add response to resources
      addResource(resourceUri, {
        name: resourceName,
        mimeType: "application/json", // Assuming JSON response
        text: JSON.stringify(data, null, 2)
      });
      
      // Format the response
      return {
        content: [{
          type: "text",
          text: JSON.stringify(data, null, 2)
        }]
      };
    } catch (error: any) {
      let errorMessage = `Error accessing JPL Horizons File API: ${error.message}`;
      if (error.response) {
        // Include more detail from the API response if available
        errorMessage += `\nStatus: ${error.response.status}\nData: ${JSON.stringify(error.response.data)}`;
      }
      return {
        content: [{
          type: "text",
          text: errorMessage
        }],
        isError: true
      };
    }
  }

• src/index.ts:1290-1347 (schema)

  Input schema and metadata definition for the `jpl_horizons_file` tool provided in the `tools/list` MCP endpoint response.

    name: "jpl_horizons_file",
    description: "JPL Horizons - Solar system objects ephemeris data (File Input)",
    inputSchema: {
      type: "object",
      properties: {
        format: {
          type: "string",
          description: "Response format (json, text)",
          enum: ["json", "text"]
        },
        COMMAND: {
          type: "string",
          description: "Target object identifier (e.g., '499' for Mars, '1' for Ceres, 'C/2020 F3' for Comet NEOWISE)"
        },
        OBJ_DATA: {
          type: "string",
          description: "Include object data",
          enum: ["YES", "NO"]
        },
        MAKE_EPHEM: {
          type: "string",
          description: "Generate ephemeris",
          enum: ["YES", "NO"]
        },
        EPHEM_TYPE: {
          type: "string",
          description: "Type of ephemeris (OBSERVER, VECTORS, ELEMENTS)",
          enum: ["OBSERVER", "VECTORS", "ELEMENTS"]
        },
        CENTER: {
          type: "string",
          description: "Coordinate center (e.g., '500@399' for Earth)"
        },
        START_TIME: {
          type: "string",
          description: "Start time for ephemeris (e.g., '2023-01-01')"
        },
        STOP_TIME: {
          type: "string",
          description: "Stop time for ephemeris (e.g., '2023-01-02')"
        },
        STEP_SIZE: {
          type: "string",
          description: "Step size for ephemeris points (e.g., '1d' for daily, '1h' for hourly)"
        },
        QUANTITIES: {
          type: "string",
          description: "Observable quantities to include (e.g., 'A' for all, or '1,2,20,23' for specific ones)"
        },
        OUT_UNITS: {
          type: "string",
          description: "Output units for vector tables",
          enum: ["KM-S", "AU-D", "KM-D"]
        }
      },
      required: ["COMMAND"]
    }
  },

• src/index.ts:1896-1932 (registration)

  Dynamic registration and dispatch logic in `handleToolCall` for JPL tools. Dynamically imports `./handlers/jpl/horizons_file.js` (endpoint='horizons_file') and executes its default export handler function.

  } else if (internalToolId.startsWith("jpl/")) {
    // Extract the JPL API endpoint name
    const endpoint = internalToolId.split("/")[1];
    serverInstance?.sendLoggingMessage({
      level: "info",
      data: `JPL Endpoint: ${endpoint}`,
    });
    
    try {
      // Dynamic import for JPL handlers using the original slash format path
      serverInstance?.sendLoggingMessage({
        level: "info",
        data: `Importing handler module: ./handlers/jpl/${endpoint}.js`,
      });
      const handlerModule = await import(`./handlers/jpl/${endpoint}.js`);
      
      // Try to find the handler function in various export formats
      const handlerFunction = handlerModule.default || 
                             handlerModule[`jpl${endpoint.charAt(0).toUpperCase() + endpoint.slice(1)}Handler`] ||
                             handlerModule[`${endpoint}Handler`];
      
      if (typeof handlerFunction === 'function') {
        return await handlerFunction(args);
      } else {
        throw new Error(`Handler for ${endpoint} not found in module`);
      }
    } catch (error: unknown) {
      const errorMessage = error instanceof Error ? error.message : String(error);
      return {
        content: [{
          type: "text",
          text: `Error executing JPL tool '${toolName}': ${errorMessage}`
        }],
        isError: true
      };
    }
  }

• src/index.ts:2151-2157 (registration)

  Global MCP tool registration for `mcp__jplhorizons_file` that routes calls to the `jpl/horizons_file` handler via `handleToolCall`.

  registerGlobalTool('mcp__jplhorizons_file', async (args: Record<string, any>) => {
    serverInstance?.sendLoggingMessage({
      level: "info",
      data: `MCP JPL Horizons File called with args: ${JSON.stringify(args)}`,
    });
    return await handleToolCall('jpl/horizons_file', args);
  });