MCP Avantage

Instructions

Implementation Reference

• src/index.ts:261-272 (registration)

  Registers the 'commodities_wheat' tool with the MCP server, including name, description, input schema from schemas.CommoditiesMonthlyQuarterlyAnnualParamsSchema, and an execute handler that uses the generic executeAvantageTool to call the AVantage library's commodities.wheat method.

  server.addTool({
    name: "commodities_wheat",
    description: "Retrieves wheat prices.",
    parameters: schemas.CommoditiesMonthlyQuarterlyAnnualParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool("commodities_wheat", args, context, (av, params) =>
        av.commodities.wheat(params)
      ),
  });

• src/schemas.ts:35-38 (schema)

  Defines the Zod input schema for the commodities_wheat tool, accepting optional 'interval' (monthly, quarterly, annual) and 'datatype' (json, csv).

  export const CommoditiesMonthlyQuarterlyAnnualParamsSchema = z.object({
    interval: MonthlyQuarterlyAnnualSchema.optional().describe('Time interval for the data.'),
    datatype: DatatypeSchema.optional().describe('Response data format.'),
  }).describe('Parameters for monthly/quarterly/annual commodity data.')

• src/index.ts:38-115 (handler)

  Generic handler function used by commodities_wheat (and all tools) to execute the AVantage library call. Manages API key resolution, AVantage instance via resourceManager, invokes the specific method (av.commodities.wheat), handles errors, and returns JSON stringified 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}`
      );
    }
  }

• src/schemas.ts:6-7 (helper)

  Supporting schema definitions: DatatypeSchema and MonthlyQuarterlyAnnualSchema used in CommoditiesMonthlyQuarterlyAnnualParamsSchema.

  const DatatypeSchema = z.enum(['json', 'csv']).describe('Data format for the response.')
  const DailyWeeklyMonthlySchema = z.enum(['daily', 'weekly', 'monthly']).describe('Time interval.')