MCP Avantage

Instructions

Implementation Reference

• src/index.ts:1255-1269 (registration)

  Registers the 'technicalIndicators_natr' MCP tool with the server, including its description, input schema, and execute handler that wraps the Alpha Vantage library call.

  server.addTool({
    name: "technicalIndicators_natr",
    description: "Normalized Average True Range (NATR)",
    parameters: schemas.TechnicalIndicatorsNatrParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool(
        "technicalIndicators_natr",
        args,
        context,
        (av, params) => av.technicalIndicators.natr(params)
      ),
  });

• src/index.ts:1259-1268 (handler)

  The execute handler function for the tool, which invokes executeAvantageTool to call the Alpha Vantage natr method with validated parameters.

  execute: (
    args,
    context // Let type be inferred
  ) =>
    executeAvantageTool(
      "technicalIndicators_natr",
      args,
      context,
      (av, params) => av.technicalIndicators.natr(params)
    ),

• src/schemas.ts:243-243 (schema)

  Defines the Zod input validation schema for the tool, aliasing the time_period-only params schema for NATR.

  export const TechnicalIndicatorsNatrParamsSchema = TechnicalIndicatorsTimePeriodOnlyParamsSchema.describe('Parameters for NATR.');

• src/index.ts:38-115 (helper)

  Shared utility function used by all Alpha Vantage tools: manages authentication, client pooling via ResourceManager, executes the specific AVantage method, handles errors, and returns JSON 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}`
      );
    }
  }