JWT Decoder

JWT Decoder splits a JSON Web Token into its three parts, header, payload, and signature, and pretty-prints the decoded claims so you can read exactly what a token contains. It's an everyday tool for debugging authentication and API integrations.

The most important thing to understand is that decoding is not verifying. A JWT's header and payload are merely Base64URL-encoded, so anyone with the token can read them, which is what this tool does. Confirming a token is authentic and untampered requires checking its signature with the signing key, something only the issuing/validating server should do.

Because the payload is readable, JWTs are signed rather than encrypted by default, and you should never place secrets in the payload. What the signature protects is integrity, it proves the claims weren't altered, not confidentiality.

Decoding runs entirely in your browser, so tokens are never transmitted; still, treat real access tokens as live credentials and prefer test or expired ones when you can. When debugging auth failures, the exp (expiry) and aud (audience) claims are usually the first things to check.