MCP Avantage

Instructions

Implementation Reference

• src/index.ts:551-565 (registration)

  Registers the 'economicIndicators_realGDP' tool with the MCP server using FastMCP. Includes name, description, input schema reference, and an inline execute handler that uses the generic executeAvantageTool to call the AVantage library's economicIndicators.realGDP method.

  server.addTool({
    name: "economicIndicators_realGDP",
    description: "Retrieves US Real Gross Domestic Product (GDP) data.",
    parameters: schemas.EconomicIndicatorsRealGDPParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool(
        "economicIndicators_realGDP",
        args,
        context,
        (av, params) => av.economicIndicators.realGDP(params)
      ),
  });

• src/schemas.ts:119-122 (schema)

  Zod schema defining the input parameters for the economicIndicators_realGDP tool: optional interval (annual/quarterly) and datatype.

  export const EconomicIndicatorsRealGDPParamsSchema = z.object({
    interval: z.enum(['annual', 'quarterly']).default('annual').optional().describe('Time interval.'),
    datatype: DatatypeSchema.default('json').optional(),
  }).describe('Parameters for fetching Real GDP data.')

• src/index.ts:38-115 (handler)

  Generic handler function shared across all tools, implementing the core execution logic: resolves API key, manages AVantage client instance via resource manager, invokes the library method specific to the tool, handles responses and errors, returns JSON string.

  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/resource-manager.ts:65-81 (helper)

  Uses resourceManager to cache and manage AVantage API client instances keyed by API key, ensuring efficient reuse and cleanup.

    const newInfo: ResourceInfo<T> = {
      resource: newResource,
      lastUsed: Date.now(),
      instanceId: instanceId,
      resourceType: resourceType,
      cacheKey: key,
      cleanupFn: cleanupFn,
    }
    this.resources.set(key, newInfo)
    logger.info(
      `Successfully created resource (Type: ${resourceType}, Instance ID: ${instanceId})`,
    )
    return newResource
  } catch (error) {
    logger.error(
      `Failed to create resource (Type: ${resourceType}) for key ${key}: ${error instanceof Error ? error.message : String(error)}`,
      error,