MCP Avantage

Instructions

Implementation Reference

• src/index.ts:583-597 (registration)

  Registers the 'economicIndicators_treasuryYield' MCP tool with the FastMCP server. Specifies the tool name, description, input schema, and an inline execute handler that uses the generic executeAvantageTool to call the AVantage library's economicIndicators.treasuryYield method.

  server.addTool({
    name: "economicIndicators_treasuryYield",
    description: "Retrieves US Treasury yield curve data for various maturities.",
    parameters: schemas.EconomicIndicatorsTreasuryYieldParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool(
        "economicIndicators_treasuryYield",
        args,
        context,
        (av, params) => av.economicIndicators.treasuryYield(params)
      ),
  });

• src/schemas.ts:128-132 (schema)

  Defines the Zod validation schema for the tool's input parameters: interval (daily, weekly, or monthly; default monthly), maturity (specific treasury bond maturities like 10year; default 10year), and datatype (json or csv; default json).

  export const EconomicIndicatorsTreasuryYieldParamsSchema = z.object({
    interval: DailyWeeklyMonthlySchema.default('monthly').optional(),
    maturity: z.enum(['3month', '2year', '5year', '7year', '10year', '30year']).default('10year').optional().describe('Treasury maturity period.'),
    datatype: DatatypeSchema.default('json').optional(),
  }).describe('Parameters for fetching Treasury Yield data.')

• src/index.ts:38-115 (handler)

  Generic handler function shared across all tools. Resolves API key, manages AVantage client instances using resourceManager, invokes the library method provided in the lambda (av.economicIndicators.treasuryYield for this tool), handles errors with UserError, and returns JSON.stringify(result.data).

  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}`
      );
    }
  }