Load Test Before You Launch — Your Agent Simulates 10,000 Users

You: Create a load test for our e-commerce API:
Endpoints: product listing, search, add to cart, checkout
Expected peak: 5,000 concurrent users
SLAs: p95 < 500ms, p99 < 1s, error rate < 0.1%
Tool preference: k6

// === load-test.js ===
import http from 'k6/http';
import { check, group, sleep } from 'k6';
import { Rate, Trend } from 'k6/metrics';

// Custom metrics
const errorRate = new Rate('errors');
const checkoutDuration = new Trend('checkout_duration');

export const options = {
  stages: [
    { duration: '2m', target: 500 },   // Warm up
    { duration: '5m', target: 2000 },   // Ramp to moderate
    { duration: '5m', target: 5000 },   // Ramp to peak
    { duration: '10m', target: 5000 },  // Sustain peak
    { duration: '3m', target: 0 },      // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500', 'p(99)<1000'],
    errors: ['rate<0.001'],
    checkout_duration: ['p(95)<2000'],
  },
};

const BASE_URL = __ENV.BASE_URL || 'https://api.myshop.com';

// Realistic user journey weights:
// 60% browse, 25% search, 10% add to cart, 5% checkout
export default function () {
  const rand = Math.random();

  if (rand < 0.60) {
    browseProducts();
  } else if (rand < 0.85) {
    searchProducts();
  } else if (rand < 0.95) {
    addToCart();
  } else {
    fullCheckout();
  }

  sleep(Math.random() * 3 + 1); // Think time: 1-4 seconds
}

function browseProducts() {
  group('Browse Products', () => {
    const res = http.get(`${BASE_URL}/v1/products?page=1&limit=20`);
    check(res, {
      'products 200': (r) => r.status === 200,
      'has results': (r) => JSON.parse(r.body).data.length > 0,
    }) || errorRate.add(1);

    // Click into a product
    sleep(0.5);
    const productRes = http.get(`${BASE_URL}/v1/products/1`);
    check(productRes, { 'product detail 200': (r) => r.status === 200 })
      || errorRate.add(1);
  });
}

// ... search, addToCart, fullCheckout functions with
// realistic data, auth headers, and validation

skills:
  - load-testing
  - monitoring    # For correlating metrics during tests