JWT Token Decoder

A JWT is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. It consists of three parts: Header (algorithm and type), Payload (claims/data), and Signature (verification). JWTs are commonly used for authentication and authorization.

To decode a JWT: 1) Paste your JWT token in the input field, 2) The tool instantly displays the decoded Header and Payload, 3) View the claims including expiration time, issuer, and custom data. Note: Decoding reveals the data but doesn't verify the signature.

Yes, decoding JWTs in the browser is safe because the payload is only Base64-encoded, not encrypted. Anyone can decode a JWT. However, this tool processes tokens entirely in your browser - they're never sent to any server, protecting your sensitive tokens.

JWTs are encoded (Base64URL), not encrypted. The payload can be read by anyone. The signature only ensures integrity (data hasn't been tampered with), not confidentiality. For sensitive data, use JWE (JSON Web Encryption) or don't include sensitive data in JWTs.

Claims are statements about the subject (user) and metadata. Standard claims include: iss (issuer), sub (subject), aud (audience), exp (expiration), iat (issued at), nbf (not before). Custom claims can include user roles, permissions, or other application-specific data.

Check the 'exp' (expiration) claim in the decoded payload. This is a Unix timestamp. Compare it with the current time: if current time > exp, the token is expired. Our decoder shows the expiration time in human-readable format and indicates if expired.

Common JWT signing algorithms include: HS256 (HMAC with SHA-256) using a shared secret, RS256 (RSA with SHA-256) using public/private key pairs, and ES256 (ECDSA with SHA-256). The algorithm is specified in the JWT header's 'alg' field.

This tool decodes and displays JWT contents but doesn't verify signatures (which requires the secret/private key). For security, always verify signatures server-side using libraries like jsonwebtoken (Node.js), PyJWT (Python), or similar.

Never store sensitive data in JWTs: passwords, credit card numbers, social security numbers, or any PII that shouldn't be exposed. Remember, JWTs can be decoded by anyone. Store only necessary claims like user ID, roles, and expiration.

JWTs are stateless (server doesn't store session data) while sessions are stateful (stored server-side). JWTs scale better across servers and work well for APIs/mobile apps. Sessions offer easier revocation and smaller token size. Many apps use a hybrid approach.