Decoding and verification are different operations. The JWT Decoder displays readable token sections. It does not establish that the issuer signed the token, that the signature is valid or that your application should accept it.
Inspect the structure
A common signed compact JWT has three dot-separated sections: header, payload and signature. Header and payload use base64url encoding. Encoding is not encryption; anyone with the token can generally read these sections. Never paste a real production bearer token into a public chat or issue report.
Work with a harmless example
Use a synthetic payload such as {"sub":"demo","role":"reader"}. Editing a payload can still leave readable JSON. That demonstrates why displayed claims are not proof of authenticity: acceptance requires verification with the correct key and algorithm.
Expiration is one check
An exp claim typically uses seconds since the Unix epoch. Convert seconds, not milliseconds. A future expiration does not establish the correct issuer, audience, signature or authorization. Clock tolerance and acceptance policies belong to the validating system.
Use a maintained verification library in application code, restrict accepted algorithms and keys, and validate required claims. See RFC 7519. The local decoder is an inspection aid, not an authentication decision.