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How to Load Test an API from Postman

3 min read
Loadcurl
Loadcurl
Loadcurl Team

Postman is excellent for building and debugging one HTTP request. It is not a load generator. The fastest path to a trustworthy RPS run is: perfect the call in Postman, then replay it under a controlled load profile.

Why Postman alone is not enough​

Collection Runner and simple scripts can fire many requests, but they rarely give you:

  • Precise target RPS with ramp-up
  • Clean p95 / p99 under sustained hold
  • Throughput vs target and HTTP outcome mix in one report
  • Cloud generators that are not capped by your laptop

Treat Postman as the authoring tool. Treat a load dashboard as the measurement tool.

Step 1: Make the request correct in Postman​

On staging (preferred):

  1. Method, URL, query params, headers, and JSON body match production shape
  2. Auth works (Bearer, API key, etc.)
  3. You get the expected status code and body
  4. Secrets are staging-scoped — not production admin tokens

Save that request. You will reuse the same shape under load.

Step 2: Get a pasteable snippet​

Depending on your Postman version:

  • Code snippet → cURL from the request, or
  • Copy as curl / export the HTTP details your team already shares

Loadcurl’s composer accepts curl / Postman paste and fills method, URL, headers, params, and body for you. You can also fill those fields manually on New test.

Step 3: Verify the hostname in Loadcurl​

Loadcurl only sends traffic to hosts your workspace has verified. Open Domains, add the hostname from your Postman URL (or paste the full URL — only the host is kept), then verify with DNS TXT or HTTP file.

Verifying example.com also covers api.example.com. Personal workspaces: 1 domain. Company: up to 10.

Details: Verify a domain.

Step 4: Paste into New test and set the load profile​

  1. Sign in at app.loadcurl.com
  2. Open New test
  3. Paste the Postman/curl snippet (or fill the form)
  4. Set duration, ramp-up, and target RPS within your plan caps
  5. Start — the app checks remaining quota first (duration × RPS hold)

Each Loadcurl test is one HTTP request repeated under that profile (no multi-step Postman collections yet).

Step 5: Watch the run and read the report​

The run page polls about every 3 seconds through pending → provisioned → running. When it finishes you get:

  • Request summary (2xx–5xx, timeouts, success rates)
  • Throughput vs target RPS
  • Latency percentiles (p50–p99), often by scope (all / completed / successful)
  • PDF download for sharing

See How to Read an API Load Test Report.

Postman collection tips that transfer cleanly​

  • Prefer environment variables resolved before you copy curl (so the pasted URL is concrete)
  • Avoid Postman-only pre-request scripts that mint tokens unless you also set the final header in the paste
  • Keep body JSON identical to what you validated
  • Name the Loadcurl test after the Postman request so history stays searchable

Common mistakes​

  • Pasting a production URL you have not verified (or should not load-test)
  • Skipping ramp-up after a gentle Postman check
  • Judging success only by Collection Runner “pass” counts instead of p95/p99
  • Forgetting quota: a 600s × 200 RPS run holds 120,000 requests
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