JWT Decoder & Token Inspector
Fast, secure, 100% client-side JSON Web Token (JWT) decoder. Inspect claims (sub, iss, exp, iat), token expiration countdown, and header metadata without server risk.
JSON Web Token (JWT) Architecture, Security Claims & Inspection
Client-side debugging reference for RFC 7519 tokens, OAuth 2.0 bearer authorization, and claim validation.
A JSON Web Token (JWT), defined in RFC 7519, is an open, industry-standard RFC method for representing claims securely between two parties. Compact, URL-safe, and digitally signed, JWTs are used ubiquitously in modern single-page applications, mobile backends, microservices, and OAuth 2.0 / OpenID Connect identity flows.
How It Works & Underlying Architecture
A serialized JWT consists of three segments separated by periods: Header.Payload.Signature. The Header specifies the cryptographic signing algorithm (such as HS256 for symmetric secrets or RS256 for asymmetric public/private key pairs). The Payload contains registered claims (iss, sub, aud, exp, nbf, iat) and custom application data. Our tool decodes Base64URL encoding natively in the browser, displays formatted JSON, calculates remaining expiration time, and highlights security warnings.
Technical Specifications & Standards
| Standards | RFC 7519 (JWT), RFC 7515 (JWS), RFC 7518 (JWA) |
| Supported Algorithms | HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, EdDSA |
| Execution Environment | 100% Client-Side Web Sandbox (Zero Server Latency) |
Real-World Engineering & Creative Use Cases
- API Troubleshooting: Inspecting user roles, permissions, and tenant IDs embedded inside access tokens.
- Expiration Verification: Debugging token expiration issues and clock-skew synchronization between client and auth server.
- Security Auditing: Checking for insecure algorithms (such as the deprecated alg:none vulnerability).
Frequently Asked Questions (FAQ)
Is it safe to paste confidential production JWTs into this tool?
Yes. All decoding runs strictly inside your local browser memory via JavaScript. No tokens, headers, or claims are ever transmitted across the internet.
Are JWT payloads encrypted?
No. JWT payloads are Base64URL encoded, not encrypted. Anyone who intercepts the token can read all claims. Sensitive passwords or keys should never be stored in standard JWT payloads unless encrypted via JWE (RFC 7516).