MCP Avantage

Instructions

Implementation Reference

• src/index.ts:1427-1441 (registration)

  MCP tool registration for 'technicalIndicators_minusDM', including name, description, input schema reference, and execute handler that delegates to Alpha Vantage library via executeAvantageTool.
  server.addTool({ name: "technicalIndicators_minusDM", description: "Minus Directional Movement (-DM)", parameters: schemas.TechnicalIndicatorsMinusDmParamsSchema, execute: ( args, context // Let type be inferred ) => executeAvantageTool( "technicalIndicators_minusDM", args, context, (av, params) => av.technicalIndicators.minusDM(params) ), });
• src/schemas.ts:250-250 (schema)

  Schema definition for the tool's input parameters, referencing the base time-period schema with specific description.
  export const TechnicalIndicatorsMinusDmParamsSchema = TechnicalIndicatorsTimePeriodOnlyParamsSchema.describe('Parameters for MINUS_DM.');
• src/index.ts:38-115 (helper)

  Shared utility function that orchestrates the execution of Alpha Vantage tools: manages API key, creates/reuses AVantage client via resource manager, invokes the specific method (e.g., technicalIndicators.minusDM), and returns JSON stringified data or errors appropriately for MCP.
  async function executeAvantageTool<TArgs, TResult>( toolName: string, args: TArgs, context: Context<Record<string, unknown> | undefined>, // Use the imported Context type directly avantageMethod: ( av: AVantage, args: TArgs ) => Promise<{ error?: boolean; reason?: string; data?: TResult }> ): Promise<string> { logger.info(`Executing '${toolName}' tool for request ID: ${context}`); logger.debug(`Args for ${toolName}: ${JSON.stringify(args)}`); // --- Authentication & Resource Management --- // Access extraArgs safely - it might be null or undefined const extraArgsApiKey = context.extraArgs?.apiKey as string | undefined; const apiKey = extraArgsApiKey || config.apiKey; if (!apiKey) { logger.error(`'${toolName}' failed: Alpha Vantage API key missing.`); throw new UserError(apiKeyErrorMessage); } logger.debug( `Using AV API key (source: ${extraArgsApiKey ? "extraArgs" : "environment"}) for ${toolName}` ); try { // Get or create AVantage instance managed by ResourceManager const av = await resourceManager.getResource<AVantage>( apiKey, // Cache key is the resolved API key "avantage_client", // Type identifier for logging async (key) => { // Factory Function logger.info( `Creating new AVantage instance for key ending ...${key.slice(-4)}` ); // AVantage library reads AV_PREMIUM from process.env internally return new AVantage(key); }, async (avInstance) => { // Cleanup Function (no-op needed for AVantage) logger.debug(`Destroying AVantage instance (no-op)`); } ); // --- Library Call --- const result = await avantageMethod(av, args); // --- Response Handling --- if (result.error) { logger.warn( `'${toolName}' failed. Reason from avantage: ${result.reason}` ); throw new UserError(result.reason || `Tool '${toolName}' failed.`); } if (result.data === undefined || result.data === null) { logger.warn(`'${toolName}' completed successfully but returned no data.`); return "null"; // Return string "null" for empty data } logger.info(`'${toolName}' completed successfully.`); // Stringify the data part of the response return JSON.stringify(result.data); } catch (error: any) { logger.error( `Error during execution of '${toolName}': ${error.message}`, error ); // If it's already a UserError, rethrow it if (error instanceof UserError) { throw error; } // Otherwise, wrap it in a UserError throw new UserError( `An unexpected error occurred while executing tool '${toolName}': ${error.message}` ); } }