How to Test APIs in Vibecoded Apps

Use a tool like Postman, Insomnia, or cURL to test each API endpoint independently from the UI. Start with GET requests and verify the response structure matches what the frontend expects. AI-generated APIs often return inconsistent response shapes — an endpoint might return an array when there are results but null or an empty object when there are none.

Check HTTP status codes carefully. A common vibecoded bug is returning 200 OK for every response, even errors. Successful operations should return 200 or 201, not-found should return 404, validation errors should return 400, and unauthorized requests should return 401 or 403. Verify the response body includes useful error messages, not just status codes.

Send unexpected input to every endpoint: missing required fields, wrong data types, extremely large payloads, and malformed JSON. AI-generated backend code frequently crashes or returns 500 errors on unexpected input instead of validation errors. Every endpoint should gracefully reject bad input with a descriptive error.

Test query parameters and URL parameters with special characters, empty strings, and SQL injection payloads. Even if you are using an ORM that prevents SQL injection, testing confirms there are no raw query backdoors. Also test pagination parameters with negative numbers, zero, and extremely large page sizes.

Verify that rate limiting is in place and working. Send rapid bursts of requests and confirm you receive 429 Too Many Requests after exceeding the limit. Many AI-generated apps have no rate limiting at all, which makes them vulnerable to abuse and denial-of-service.

Test authorization on every endpoint. Remove or modify the auth token and verify that protected endpoints return 401. Test with a valid token from a different user and confirm you cannot access another user's data. This cross-user access testing is critical because AI tools often implement auth on the login endpoint but forget to protect individual API routes.