Launch day is the worst time to find out how many users your API can serve. A load test a week earlier answers the same question while you can still act on it. Here's one you can run in an afternoon.

1. Write down what "ready" means

Three numbers, before you send a single request:

Expected peak: 2,000 visitors in the launch hour × ~30 API calls each ≈ 17 requests/s on average. Peaks run 2–3× higher, so plan for 50 requests/s.

Latency goal: p95 under 500 ms .

Error goal: under 1% failed requests.

These become pass/fail thresholds. Without them a load test produces charts, not a decision.

2. Test a journey, not an endpoint

Real users don't call GET /health in a loop. They:

POST /login , and keep the token

GET /products?page=1

GET /products/{id} for an id from the list

POST /cart with that product

Pass values from step to step, use many test accounts , and add think time between steps.

3.…