API Security Testing Guide

Start with scope and a question

Before sending any request, confirm that you own the target or have written permission to test it. Define the endpoints, credentials, traffic limits, test window, and success criteria. A focused question produces more useful evidence than an unbounded scan.

API security assessment

Review transport security, headers, authentication, authorization, input validation, error handling, exposed information, and common vulnerability patterns. Treat automated findings as leads: reproduce important results, assess impact, and confirm the affected code or configuration before remediation.

Load and performance testing

Use a load test when the question concerns a planned request volume. Use a performance test when the question concerns behavior over time. Compare successful responses, errors, throughput, average latency, P50, and P95 under the same conditions. Increase concurrency gradually and stop if the target becomes unstable.

Interpret results and retest

Record the target, test settings, build version, environment, timestamps, and observed results. Prioritize security findings by impact and exploitability. For performance work, compare against a baseline rather than relying on one metric. After a fix, repeat the same test so the change can be evaluated.

Authorized testing only: do not scan or generate traffic against systems without permission.