5 min read
2026-02-17
If there are problems with authorization, the first step is to decode the token and check its contents: roles, rights, expiration date.
When integrating with third-party services (Auth0, Firebase, Keycloak), it is useful to study the token structure.
| Symptom | JWT problem |
|---|---|
| 401 Unauthorized | Expired Token |
| 403 Forbidden | No required role |
| Parsing error | Damaged token |
| Invalid user | Incorrect sub claim |
When manually testing an API via Postman or cURL, it is convenient to decode the received tokens for verification.
When changing authentication providers, compare the token structure to ensure compatibility.
###Security monitoring
Periodic analysis of tokens helps to detect anomalies: too long TTL, unnecessary claims, suspicious algorithms.
JWT Decoder visualizes the structure of a token, making it an excellent learning tool.
See also: HTTP status codes, MIME Types, JSON Formatter