How to Write Scripts to Validate API Response Data

When you’re testing APIs inside an API client, sending the request is only half the job. The real question is: did the response actually match what you expected? That’s where post-response scripts come in. A post script runs immediately after the API response is received. You can use it to validate status codes, check response structure, confirm required fields, and fail fast if something looks wrong. Instead of manually inspecting every response, you let the script do the checking for you. Why Use Post-Response Scripts? Manually scanning JSON works for quick debugging. It doesn’t scale. Post scripts help you: Catch contract changes early Validate required fields automatically Confirm response types and formats Verify error handling Prevent silent test failures Reuse validation logic across requests If something breaks, you know immediately. Basic Response Validation Example Let’s say your API should: Return status 200 Contain a user object Include an items array Here’s a simple valida