retrylab.dev is a free tool for testing retry logic. one url that fails exactly how you tell it to, no signup
bash
id=$(curl -s -X POST https://retrylab.dev/api/sessions \ -H 'Content-Type: application/json' -d '{"fail":3,"code":503}' | jq -r .id) for i in 1 2 3 4; do curl -s -o /dev/null -w '%{http_code}\n' https://retrylab.dev/api/e/$id/test; done # 503 503 503 200

RetryLabRetryLab - Test API test EndpointConfigure failure scenarios for test endpoint. Test timeouts, error codes, and retry logic.
commit 4e3f15b