TfL Journey Status MCP Server

Instructions

Implementation Reference

• tools/tfl/status.js:9-39 (handler)

  The core handler function `executeFunction` that fetches the current status of a specified TfL line from the TfL API, handling parameters and errors.

  const executeFunction = async ({ lineId, app_key }) => {
    if (!lineId) {
      throw new Error('lineId is required');
    }
  
    const params = new URLSearchParams();
    if (app_key) {
      params.append('app_key', app_key);
    }
  
    const query = params.toString();
    const url = `https://api.tfl.gov.uk/Line/${encodeURIComponent(lineId)}/Status${query ? `?${query}` : ''}`;
  
    try {
      const response = await fetch(url, {
        method: 'GET'
      });
  
      if (!response.ok) {
        const errorData = await response.json();
        throw new Error(JSON.stringify(errorData));
      }
  
      return await response.json();
    } catch (error) {
      console.error('Error fetching the status:', error);
      return {
        error: `An error occurred while fetching the status: ${error instanceof Error ? error.message : JSON.stringify(error)}`
      };
    }
  };

• tools/tfl/status.js:45-68 (schema)

  The `apiTool` object defining the tool's schema, including name, description, input parameters schema with lineId required and app_key optional.

  const apiTool = {
    function: executeFunction,
    definition: {
      type: 'function',
      function: {
        name: 'get_line_status',
        description: 'Get the status of a TfL line from the Transport for London Unified API.',
        parameters: {
          type: 'object',
          properties: {
            lineId: {
              type: 'string',
              description: 'The identifier of the line to query (e.g., victoria, central).'
            },
            app_key: {
              type: 'string',
              description: 'Optional application key for the API.'
            }
          },
          required: ['lineId']
        }
      }
    }
  };

• lib/tools.js:7-30 (registration)

  The `discoverTools` function that dynamically loads the `apiTool` exports from tool files listed in toolPaths, enabling registration of get_line_status among others for the MCP server.

  export async function discoverTools() {
    const tools = await Promise.all(
      toolPaths.map(async (file) => {
        const { apiTool } = await import(`../tools/${file}`);
        return { ...apiTool, path: file };
      })
    );
  
    // deduplicate tool names
    const nameCounts = {};
  
    return tools.map((tool) => {
      const name = tool.definition?.function?.name;
      if (!name) return tool;
  
      nameCounts[name] = (nameCounts[name] || 0) + 1;
  
      if (nameCounts[name] > 1) {
        tool.definition.function.name = `${name}_${nameCounts[name]}`;
      }
  
      return tool;
    });
  }

• tools/paths.js:1-5 (registration)

  The `toolPaths` array listing 'tfl/status.js' which provides the get_line_status tool, used by discoverTools for automatic registration.

  export const toolPaths = [
    'tfl/status.js',
    'tfl/status-detail.js',
    'tfl/journey-planner.js'
  ];