JWT Decoder

JWT Decoder: This free tool decodes JSON Web Tokens by splitting them into header, payload, and signature segments and displaying each in readable JSON format. Paste any JWT and instantly see its algorithm, claims, expiry status, and more - all offline with no signup required ever.

How JWTs Work: A JWT consists of three base64url-encoded segments separated by dots: header (algorithm and token type), payload (claims like sub, exp, iat), and signature (for verification). This tool decodes the first two segments and reports whether a signature is present, but it cannot verify signatures without the issuer's secret key.

Expiry Checking: The tool automatically compares the exp claim against the current time and tells you whether the token is valid, expired, or has no expiry claim. This is essential for debugging authentication flows where expired tokens cause silent failures.

Security Warning: Decoding is not verifying. Anyone can create a well-formed JWT with any claims. Trust comes only from cryptographic verification with the issuer's secret or public key. This tool never sees secrets and never transmits the token - everything runs in your browser.

Common Claims: The tool shows standard claims like sub (subject), exp (expiry), iat (issued at), iss (issuer), aud (audience), and any custom claims. This is useful for debugging auth flows, checking token expiry in support tickets, and learning JWT structure safely.

Browser-Based Privacy: All decoding happens in your browser using base64url decoding and JSON parsing. No token data is sent anywhere, making this safe for production tokens (though test tokens are always preferred). The tool is completely free with no signup required ever.