Working with JSON Web Tokens? Our free JWT decoder helps you inspect and debug tokens instantly. Whether you're developing authentication systems, debugging API issues, learning about JWTs, or verifying token contents, this tool decodes the header and payload while optionally verifying signatures. Paste any JWT and see its contents in a readable format.
JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are digitally signed and optionally encrypted. They're widely used for authentication (proving identity) and authorization (determining permissions) in modern web applications, mobile apps, and APIs. A JWT compactly represents claims using a three-part structure: header.payload.signature.
Our JWT decoder provides: Automatic decoding of header and payload. Pretty-printed JSON display. Signature verification with secret/public keys. Token expiration checking. Base64URL decoding. Multiple algorithm support (HS256, RS256, ES256, etc.). Copy buttons for decoded data. JWT validation indicators. Mobile-friendly design. No data sent to servers.
The decoder splits the JWT by dots into three parts. Header and payload are Base64URL decoded to JSON. The signature remains as-is for verification. For verification: The tool recreates the signing input (header.payload), applies the algorithm with your provided key, and compares to the token's signature. Expiration is checked by comparing the exp claim to current time.
Authentication Debugging - Inspect login tokens. API Development - Testing authorization flows. Security Auditing - Reviewing token claims. Learning JWT Structure - Understanding token anatomy. Troubleshooting - Why tokens fail validation. Token Inspection - Verifying third-party tokens. Development Testing - Creating test tokens.
Our decoder offers: Instant Decoding without setup. Visual Display of structured data. Security Verification for signatures. Educational Value for learning JWTs. Debugging Help for auth issues. Privacy with client-side processing. Convenience for quick checks.
Backend Developers implementing authentication. Frontend Developers handling tokens. Security Engineers auditing systems. DevOps Engineers debugging issues. Students learning about JWTs. API Developers testing integrations. QA Engineers validating auth flows.
Paste your JWT token in the input field. View automatically decoded header and payload. Check expiration status. Optionally enter secret key to verify signature. Copy decoded data as needed.
Never Share Production Tokens online. Verify All Signatures in production code. Check Expiration before trusting claims. Use HTTPS for token transmission. Keep Secrets Secure and private. Validate All Claims appropriately.
Cannot crack or brute force secrets. Requires valid Base64URL encoding. Signature verification needs correct key. Browser-only processing.
JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. It's commonly used for authentication and information exchange. A JWT consists of three parts: Header (algorithm and token type), Payload (claims/data), and Signature (verification). The format is: header.payload.signature.
Decoding JWTs is safe because our tool works entirely client-side - your tokens are never sent to our servers. However, never paste production tokens containing sensitive data into any online tool you don't fully trust. JWTs are encoded, not encrypted, so anyone with the token can read its contents.
Decoding reads the token's contents (header and payload) which is always possible since JWTs are Base64 encoded. Verifying checks if the signature is valid using a secret key or public key, ensuring the token hasn't been tampered with. Our decoder shows decoded data; verification requires the secret key.
Common registered claims include: iss (issuer), sub (subject/user ID), aud (audience), exp (expiration time), nbf (not before), iat (issued at), jti (JWT ID). Custom claims like user roles, permissions, or app-specific data are also commonly included in the payload.
Check the 'exp' (expiration) claim in the payload. It's a Unix timestamp representing when the token expires. Compare it to the current time. Our decoder highlights expired tokens. If current time > exp, the token is expired and should be rejected by your application.
Yes, you can paste your secret key or public key to verify the signature. For HS256 (HMAC), use the shared secret. For RS256/ES256, paste the public key in PEM format. Never paste production secrets; this feature is for debugging only.
Common algorithms include: HS256 (HMAC with SHA-256 - symmetric), HS384, HS512, RS256 (RSA with SHA-256 - asymmetric), RS384, RS512, ES256 (ECDSA with SHA-256), ES384, ES512, and none (unsecured, not recommended). The algorithm is specified in the token header.
Invalid signature means: The token was modified after creation, wrong secret key was used for verification, algorithm mismatch, or the token was created with a different key pair. Always verify signatures in production to prevent token tampering attacks.