MCP Avantage

Instructions

Implementation Reference

• src/index.ts:541-547 (handler)

  The inline execute handler for the 'crypto_monthly' MCP tool. It delegates to the shared executeAvantageTool helper, which calls the Alpha Vantage crypto.monthly API method.

  execute: (
    args,
    context // Let type be inferred
  ) =>
    executeAvantageTool("crypto_monthly", args, context, (av, params) =>
      av.crypto.monthly(params)
    ),

• src/schemas.ts:112-116 (schema)

  Zod schema defining input parameters for crypto time series tools (daily/weekly/monthly), including symbol, market, and optional datatype.

  export const CryptoTimeSeriesParamsSchema = z.object({
    symbol: z.string().describe('The cryptocurrency symbol (e.g., "BTC").'),
    market: z.string().describe('The exchange market (e.g., "USD", "EUR").'),
    datatype: DatatypeSchema.default('json').optional(),
  }).describe('Parameters for fetching daily/weekly/monthly crypto time series data.')

• src/index.ts:537-548 (registration)

  MCP server tool registration for 'crypto_monthly', specifying name, description, input schema, and handler.

  server.addTool({
    name: "crypto_monthly",
    description: "Fetches monthly time series data for a cryptocurrency.",
    parameters: schemas.CryptoTimeSeriesParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool("crypto_monthly", args, context, (av, params) =>
        av.crypto.monthly(params)
      ),
  });

• src/index.ts:38-115 (helper)

  Shared utility function used by all tools to manage Alpha Vantage client instances, perform API calls via the provided method, handle authentication, errors, and return JSON string responses.

  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}`
      );
    }
  }