JWT Analyzer
Decode and analyse JSON Web Tokens — inspect claims, algorithm, expiry and security issues
Paste a JSON Web Token to decode its header and payload, review standard claims and expiry, and see warnings for weak algorithms or sensitive data in the payload. Remember that a JWT payload is only encoded, not encrypted. More free security tools.
A JSON Web Token has three Base64URL-encoded parts separated by dots: a header describing the signing algorithm, a payload carrying the claims, and a signature that proves the first two haven't been tampered with. Decoding the header and payload is pure Base64 — no secret or private key is needed, which is exactly why a JWT must never hold data you wouldn't want a client to read.
This analyzer checks the signing algorithm (flagging "none" as forgeable and symmetric HS256 as requiring a shared secret), and reviews the standard registered claims — exp, iat, nbf, iss, aud and jti — that control expiry, timing and revocation. Missing an expiry claim, using an overly long TTL, or lacking an audience claim are common findings that weaken session and API token security even when the signature itself is sound.
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