MCP Utility Tools

Instructions

Implementation Reference

• src/index-v2.ts:640-684 (handler)

  The main handler function for the 'rate_limit_check' tool. It checks if a request for a given resource is within rate limits, optionally increments the counter, and returns status including remaining requests and reset time.

  case "rate_limit_check": {
    const {
      resource,
      max_requests = 60,
      window_seconds = 60,
      increment = true
    } = args as any;
  
    const now = Date.now();
    const windowMs = window_seconds * 1000;
    
    let limit = rateLimits.get(resource);
    
    // Initialize or reset if window expired
    if (!limit || limit.resetAt <= now) {
      limit = {
        count: 0,
        resetAt: now + windowMs
      };
      rateLimits.set(resource, limit);
    }
    
    const allowed = limit.count < max_requests;
    const remaining = Math.max(0, max_requests - limit.count);
    const resetIn = Math.ceil((limit.resetAt - now) / 1000);
    
    if (allowed && increment) {
      limit.count++;
    }
    
    return {
      content: [{
        type: "text",
        text: JSON.stringify({
          allowed,
          resource,
          current_count: limit.count,
          max_requests,
          remaining,
          reset_in_seconds: resetIn,
          reset_at: new Date(limit.resetAt).toISOString()
        })
      }]
    };
  }

• src/index-v2.ts:239-267 (schema)

  The tool specification including name, description, and input schema for 'rate_limit_check', which defines the expected input parameters and validation.

  {
    name: "rate_limit_check",
    description: "Check if an operation should be rate-limited",
    inputSchema: {
      type: "object",
      properties: {
        resource: {
          type: "string",
          description: "Resource identifier (e.g., 'api.github.com')"
        },
        max_requests: {
          type: "number",
          description: "Maximum requests allowed",
          default: 60
        },
        window_seconds: {
          type: "number",
          description: "Time window in seconds",
          default: 60
        },
        increment: {
          type: "boolean",
          description: "Increment the counter if allowed",
          default: true
        }
      },
      required: ["resource"]
    }
  }

• src/index-v2.ts:270-271 (helper)

  Global storage Map for rate limit counters per resource, essential for tracking usage across tool calls.

  // Rate limiting storage
  const rateLimits = new Map<string, { count: number; resetAt: number }>();