HTTP Status Codes Used in API Testing

Problem: Quickly interpret HTTP responses when testing APIs.

Common codes

200 OK

Successful request; inspect body for expected data.

201 Created

Resource created; check Location header and response body.

400 Bad Request

Client-side validation issue — check payload and parameters.

401 Unauthorized

Authentication required or token invalid/expired.

403 Forbidden

Authenticated but not authorized to perform the action.

404 Not Found

Resource does not exist or wrong URL.

500 Internal Server Error

Server-side error — collect logs and request details for debugging.

Practical tips

• When seeing 401, decode the JWT to inspect expiry or scopes using JWT Decoder.
• For 400, validate JSON with JSON Formatter.