JWT Decoder

Free JWT Decoder

Decode and inspect JSON Web Tokens instantly. View header, payload and signature. Check expiration status. No data sent to servers.

Paste a JWT token into the input field and the tool immediately splits it into three parts: header, payload, and signature. Each section decodes from Base64 and displays as formatted JSON showing all claims and metadata. The payload section highlights standard claims like issuer, expiration, and issued-at times. If the token includes an expiration claim, the tool indicates whether it's expired, valid, or not yet active. The signature portion displays as a Base64 string since verifying it requires the secret key. All decoding happens in your browser without sending the token to any server.

Frontend developers inspect JWT tokens stored in browser localStorage to debug authentication issues and verify claim contents. Backend engineers examine tokens returned from OAuth providers to understand what user information is included. Security auditors analyze JWT tokens during penetration testing to look for sensitive data leakage in claims. Mobile app developers decode tokens from API responses to troubleshoot session management problems.

Decoding a JWT doesn't verify its signature, so a decoded token might still be invalid or tampered with—always verify signatures server-side before trusting claims. Check the expiration claim (exp) in the payload; expired tokens should be rejected even if they decode successfully. Look for sensitive information in the payload like passwords or PII, which should never be in JWTs since they're only encoded, not encrypted. The 'alg' field in the header tells you which algorithm signed the token; 'none' is a security red flag indicating the token has no signature verification.

All processing happens directly in your browser. Your files never leave your device — no server uploads, no cloud storage, no data retention. The tool works offline once loaded, requires no registration, and is completely free with no usage limits.