JSON Web Tokens carry claims between systems. Decoding is not the same as trusting a signature.
Three parts
A JWT is three Base64URL segments: header, payload, and signature. The payload holds claims such as subject and expiry. The signature is how a server proves the claims were not edited.
Authentication versus inspection
Logging in with JWT means the server verified the signature with a secret or public key. Pasting a token into a decoder only reads the claims. Anyone can decode a JWT. Not everyone can forge a valid signature.
Keep tokens off servers you do not run
Treat a JWT like a password. The DNVERSE JWT Decoder never sends the token to the backend. Still avoid pasting production tokens on a shared computer.