What Is JWT: Token Structure and Security Essentials
A JWT has three parts: header (algorithm), payload (data), and signature, separated by dots. In the payload, exp is expiry and iat is issued-at time.
How to debug
- Paste the token into a decoder to see the payload
- Check whether exp has expired
- Confirm the algorithm header matches expectations
Security reminder
Anyone can decode and read a JWT — don't put passwords or sensitive info inside; security comes from the signature, not from 'others can't read it.'
💡 FreeToolset's JWT decoder runs entirely in your browser — tokens aren't uploaded, making login debugging safer.