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How to Perform Load Testing Using cURL

3 min read
Loadcurl
Loadcurl
Loadcurl Team

curl is the universal language of HTTP. Developers copy it from docs, browsers, and gateways. That makes it a natural starting point for API load testing — but curl alone is not a load generator.

Here is how to use curl the right way: debug with it, then scale with a proper load profile.

What curl is good at​

  • Reproducing a single failing request
  • Confirming auth headers and status codes
  • Timing one call with -w / -o
  • Exporting a canonical request teammates can paste

Example:

curl -sS -X POST 'https://api.example.com/v1/orders' \
  -H 'Authorization: Bearer TOKEN' \
  -H 'Content-Type: application/json' \
  -d '{"sku":"sku_123","qty":1}'

What curl is bad at (for load)​

Naive loops like for i in {1..1000}; do curl ...; done are not load tests:

  • They are usually sequential, not concurrent
  • They do not control RPS precisely
  • They skew latency with client overhead
  • They rarely produce p95/p99 or throughput reports
  • Your laptop becomes the bottleneck quickly

Shell parallelism (xargs -P, background jobs) is still a rough hammer — fine for a smoke blast, weak for capacity claims.

A practical workflow: curl → load test​

1. Perfect one request with curl​

Make sure the call returns the expected status and body on staging. Fix auth, headers, and JSON first.

2. Capture the curl (or Postman) snippet​

Keep it as the source of truth for the request shape.

3. Paste into a load testing dashboard​

Tools like Loadcurl accept curl / Postman paste into the composer, then let you set:

  • Target RPS
  • Ramp-up
  • Duration

Cloud generators send the traffic; you are not installing workers. You must verify the domain before runs can target that host.

4. Read percentiles and HTTP outcomes​

Judge the run on p95/p99, achieved RPS vs target, and error/timeout rates — not on how fast your shell loop felt.

Timing a single request with curl​

For quick local checks:

curl -sS -o /dev/null -w 'time_total=%{time_total}\nhttp_code=%{http_code}\n' \
  'https://staging.example.com/health'

Useful for debugging. Not a substitute for a multi-minute RPS hold.

Security and safety​

  • Prefer staging tokens in curl history and shared snippets
  • Do not load test hosts you do not own
  • Strip secrets before pasting into tickets; rotate if leaked
  • Ramp up; production traffic is real

Curl + Loadcurl in practice​

  1. Register at app.loadcurl.com
  2. Verify your domain (docs)
  3. Open New test and paste your curl
  4. Set RPS, ramp-up, duration
  5. Start — the run page polls live status about every 3 seconds
  6. Download the report PDF when finished

This keeps curl as the authoring format while cloud infrastructure handles concurrency and reporting.

When to stay local vs go cloud​

Stay local for functional curl debugging. Move to cloud generators when you need sustained RPS, clean percentiles, and isolation from laptop limits — covered in Cloud-Based vs Local Load Testing.

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