MCP Avantage

Instructions

Implementation Reference

• src/index.ts:998-1012 (registration)

  Registers the MCP tool 'technicalIndicators_ema' with server.addTool, including name, description, parameters schema from schemas.TechnicalIndicatorsTimeSeriesIndicatorParamsSchema, and an execute handler that delegates to executeAvantageTool calling the AVantage library's ema method.

  server.addTool({
    name: "technicalIndicators_ema",
    description: "Exponential Moving Average (EMA)",
    parameters: schemas.TechnicalIndicatorsTimeSeriesIndicatorParamsSchema,
    execute: (
      args,
      context // Let type be inferred
    ) =>
      executeAvantageTool(
        "technicalIndicators_ema",
        args,
        context,
        (av, params) => av.technicalIndicators.ema(params)
      ),
  });

• src/schemas.ts:204-215 (schema)

  Defines TechnicalIndicatorsCommonIndicatorParamsSchema (base parameters: symbol, interval, etc.) extended by TechnicalIndicatorsTimeSeriesIndicatorParamsSchema adding time_period and series_type, which validates the input for the technicalIndicators_ema tool.

  export const TechnicalIndicatorsCommonIndicatorParamsSchema = z.object({
    symbol: z.string().describe('The stock symbol (e.g., "IBM").'),
    interval: z.string().describe('Time interval (e.g., "daily", "60min", "weekly"). Check Alpha Vantage docs for valid intervals per indicator.'),
    datatype: DatatypeSchema.default('json').optional(),
    month: z.string().optional().describe('Specific month for intraday intervals (YYYY-MM format).'),
  }).describe('Common parameters for many technical indicators.')
  
  // Schema for indicators requiring time_period and series_type
  export const TechnicalIndicatorsTimeSeriesIndicatorParamsSchema = TechnicalIndicatorsCommonIndicatorParamsSchema.extend({
    time_period: z.string().describe('Number of data points used to calculate the indicator.'), // Using string as AV API expects string
    series_type: SeriesTypeSchema,
  }).describe('Parameters for time series based technical indicators.')

• src/index.ts:38-115 (handler)

  Generic executeAvantageTool function that implements the tool execution logic shared by all tools: resolves API key, manages AVantage client via resourceManager, invokes av.technicalIndicators.ema(params) for this tool, stringifies the result, and handles errors.

  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:21-192 (helper)

  ResourceManager class used by executeAvantageTool to cache and lifecycle-manage AVantage API client instances keyed by API key, ensuring efficient reuse and cleanup.

  export class ResourceManager {
    private resources: Map<string, ResourceInfo<any>> = new Map()
    private readonly cleanupIntervalMs: number
    private cleanupTimer: NodeJS.Timeout | null = null
  
    constructor(options?: { cleanupIntervalMs?: number }) {
      this.cleanupIntervalMs =
        options?.cleanupIntervalMs ?? config.resourceCleanupInterval
      this.startCleanupTimer()
      logger.info(
        `ResourceManager initialized. Cleanup interval: ${this.cleanupIntervalMs}ms`,
      )
    }
  
    /**
     * Retrieves an existing resource or creates a new one.
     */
    public async getResource<T>(
      key: string,
      resourceType: string,
      factoryFn: (key: string) => Promise<T>,
      cleanupFn: (resource: T) => Promise<void>,
    ): Promise<T> {
      const existingInfo = this.resources.get(key)
  
      if (existingInfo) {
        logger.debug(
          `Reusing existing resource (Type: ${existingInfo.resourceType}, Instance ID: ${existingInfo.instanceId}) for key ending with ...${key.slice(-4)}`,
        )
        existingInfo.lastUsed = Date.now()
        if (existingInfo.resourceType !== resourceType) {
          logger.warn(
            `Resource type mismatch for key ${key}. Expected ${resourceType}, found ${existingInfo.resourceType}. Returning existing resource anyway.`,
          )
        }
        return existingInfo.resource as T
      }
  
      logger.info(
        `Creating new resource (Type: ${resourceType}) for key ending with ...${key.slice(-4)}`,
      )
      try {
        const newResource = await factoryFn(key)
        const instanceId = uuidv4()
        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,
        )
        throw new Error(
          `Resource factory function failed for type ${resourceType}: ${error instanceof Error ? error.message : String(error)}`,
        )
      }
    }
  
    private startCleanupTimer(): void {
      if (this.cleanupTimer) {
        clearInterval(this.cleanupTimer)
      }
      this.cleanupTimer = setInterval(
        () => this.cleanupInactiveResources(),
        this.cleanupIntervalMs,
      )
      this.cleanupTimer.unref()
      logger.info('Resource cleanup timer started.')
    }
  
    public stopCleanupTimer(): void {
      if (this.cleanupTimer) {
        clearInterval(this.cleanupTimer)
        this.cleanupTimer = null
        logger.info('Resource cleanup timer stopped.')
      }
    }
  
    private async cleanupInactiveResources(): Promise<void> {
      const now = Date.now()
      let cleanedCount = 0
      logger.debug('Running inactive resource cleanup check...')
  
      const keysToRemove: string[] = []
      for (const [key, info] of this.resources.entries()) {
        if (now - info.lastUsed > this.cleanupIntervalMs) {
          keysToRemove.push(key)
        }
      }
  
      if (keysToRemove.length === 0) {
        logger.debug('No inactive resources found to clean up.')
        return
      }
  
      logger.info(`Found ${keysToRemove.length} inactive resource(s) to clean up.`)
  
      for (const key of keysToRemove) {
        const info = this.resources.get(key)
        // Double-check inactivity before removing, in case it was accessed again
        if (info && now - info.lastUsed > this.cleanupIntervalMs) {
          logger.info(
            `Cleaning up inactive resource (Type: ${info.resourceType}, Instance ID: ${info.instanceId}, Key: ...${key.slice(-4)})`,
          )
          try {
            await info.cleanupFn(info.resource)
            this.resources.delete(key)
            cleanedCount++
            logger.info(
              `Successfully cleaned up resource (Instance ID: ${info.instanceId})`,
            )
          } catch (error) {
            logger.error(
              `Error during cleanup of resource (Instance ID: ${info.instanceId}): ${error instanceof Error ? error.message : String(error)}`,
              error,
            )
            // Optionally remove from map even if cleanup failed
            // this.resources.delete(key);
          }
        }
      }
  
      if (cleanedCount > 0) {
        logger.info(`Finished cleanup. Removed ${cleanedCount} inactive resource(s).`)
      } else {
        logger.debug('Finished cleanup check, no resources were removed this cycle.')
      }
    }
  
    /**
     * Immediately destroys all managed resources. Useful for graceful shutdown.
     */
    public async destroyAllNow(): Promise<void> {
      logger.warn('Destroying all managed resources immediately...')
      this.stopCleanupTimer()
  
      const cleanupPromises: Promise<void>[] = []
      for (const [key, info] of this.resources.entries()) {
        logger.info(
          `Initiating immediate cleanup for resource (Type: ${info.resourceType}, Instance ID: ${info.instanceId}, Key: ...${key.slice(-4)})`,
        )
        cleanupPromises.push(
          info
            .cleanupFn(info.resource)
            .catch((error) =>
              logger.error(
                `Error during immediate cleanup of resource (Instance ID: ${info.instanceId}): ${error instanceof Error ? error.message : String(error)}`,
                error,
              ),
            ),
        )
      }
  
      await Promise.allSettled(cleanupPromises)
  
      const finalCount = this.resources.size
      this.resources.clear()
      logger.warn(
        `Finished destroying all resources. Cleared ${finalCount} resource entries.`,
      )
    }
  }