MCP Tools for AI Agents: How to Build Production-Grade Integrations

MCP is a protocol that lets AI agents discover and invoke external tools through a standardized interface. Instead of hardcoding API calls into your agent's prompt, you define tools as structured schemas:

{
  "name": "create_checkout_session",
  "description": "Create a Stripe checkout session for a product",
  "parameters": {
    "type": "object",
    "properties": {
      "priceCents": { "type": "number" },
      "currency": { "type": "string" },
      "productName": { "type": "string" }
    },
    "required": ["priceCents", "currency"]
  }
}

The agent calls this tool, the MCP server executes it, and returns structured results. Clean separation of concerns.

Stripe's API is well-designed, but there are subtleties when wrapping it for AI agents:

Idempotency keys are mandatory. AI agents retry. Network hiccups happen. Every Stripe API call should include an idempotency key:

async createCheckoutSession(params: CheckoutParams) {
  const idempotencyKey = `checkout_${params.orderId}`;
  return this.stripe.checkout.sessions.create({
      line_items: [{ price_data: {
            currency: params.currency,
            product_data: { name: params.productName },
            unit_amount: params.priceCents,
          }, quantity: 1 }],
      mode: 'payment',
      metadata: { orderId: params.orderId, type: params.type },
      success_url: `${PUBLIC_URL}/success?order=${params.orderId}`,
      cancel_url: `${PUBLIC_URL}/cancel`,
    }, { idempotencyKey });
}

Webhook verification is critical. Always verify the Stripe signature before processing:

const event = stripe.webhooks.constructEvent(body, sig, webhookSecret);

Metadata is your friend. Store business logic context in Stripe metadata — it comes back in webhooks and lets you route events to the right handler.

The X API v2 has strict rate limits and requires OAuth 1.0a. Key lessons:

Rate limit tracking. X returns x-rate-limit-reset headers. Track them in memory and wait before retrying:

if (response.status === 429) {
  const resetAt = parseInt(response.headers.get('x-rate-limit-reset') || '0');
  const waitMs = Math.max(0, resetAt * 1000 - Date.now()) + 1000;
  await sleep(waitMs);
  return this.postTweet(text); // Retry
}

Idempotency via tweet IDs. Store every posted tweet ID in your database. Before posting, check if you already posted this content. X doesn't have built-in idempotency.

Simulation mode. When API keys are missing (development, testing), the MCP should return realistic fake responses instead of crashing:

if (!this.apiKey) {
  return { id: `sim_${Date.now()}`, text, simulated: true };
}

For agents that interact with blockchains (Base L2, Ethereum), the MCP pattern is especially useful:

Separate signing from sending. The MCP should handle transaction construction, gas estimation, and signing internally, but expose a clean burn() or transfer() interface.

Gas estimation with buffer. Always add 20% buffer to gas estimates:

const gasEstimate = await publicClient.estimateGas(tx);
const gasWithBuffer = gasEstimate * 120n / 100n;

Nonce management. For concurrent transactions, track nonces locally to avoid conflicts.

Reddit's OAuth2 flow for script apps is straightforward but has quirks:

Token caching. Reddit tokens expire in 1 hour. Cache them and refresh proactively:

async getToken() {
  if (this.token && this.tokenExpiry > Date.now()) {
    return this.token;
  }
  // Refresh token...
}

User-Agent requirements. Reddit requires a descriptive User-Agent. Using the default will get you rate-limited or banned.

Error Recovery

Every MCP should implement a circuit breaker pattern. After N consecutive failures, stop calling the API for a cooldown period:

if (this.consecutiveErrors >= MAX_ERRORS) {
  if (Date.now() < this.circuitOpenUntil) {
    throw new Error('Circuit breaker open');
  }
  this.consecutiveErrors = 0; // Half-open: try again
}

Cost Tracking

If your MCP calls paid APIs (LLMs, Stripe, blockchain gas), track costs per operation:

const cost = this.estimateCost(response);
await this.traceService.record({
    task: 'stripe_checkout',
    model: 'stripe-api',
    costUsd: cost,
    tokens: 0,
});

Logging

Every MCP operation should be logged with: timestamp, operation name, input params (sanitized), output summary, duration, and cost. This is critical for debugging autonomous agents that run without supervision.

Test each MCP in three modes:

• Unit tests with mocked API responses
• Integration tests against sandbox/test environments
• Simulation tests with the harness (no real API calls)

The simulation mode is crucial for CI/CD — you don't want your test suite making real Stripe charges or posting real tweets.

We're building a marketplace for production-grade MCP integrations at Claw Mart. If you've built an MCP that handles a real-world integration with proper error handling, rate limiting, and idempotency, we'd love to feature it.

Good MCPs are the difference between an AI agent that works in a demo and one that works in production. Build them right.