Free Online JWT Decoder & Token Claims Inspector
Decode, inspect, and verify JSON Web Tokens (RFC 7519) in browser memory with color-coded syntax highlighting, live expiration telemetry, and zero server logging.
Direct Answer & Pipeline Overview
JWT Decoder & Token Claims Inspector is a specialized, 100% client-side engineering utility developed by Atlyxen Studios. It processes calculations and conversions directly inside your browser memory using hardware-accelerated WebAssembly and WebGL, guaranteeing instant results with zero server file transfers and zero data retention.
How to Use the JWT Decoder & Token Claims Inspector
Paste Encoded JWT
Copy your JSON Web Token string from your authorization header or local storage.
Inspect Claims & Header
View formatted JSON payloads, examine sub, iss, and aud claims, and verify expiry dates.
Verify HMAC Signature (Optional)
Provide your HS256 secret key to cryptographically verify token integrity locally.
Key Technical Capabilities
Color coded 3 part token decomposition: Header (red), Payload claims (cyan), and Signature (emerald)
Live expiration calculator with human readable UTC date and countdown timers
Cryptographic HMAC SHA-256 signature verification directly via Web Crypto API
Security audit heuristics detecting "alg": "none" and deprecated algorithms
Quick presets for active, expired, and role based access control (RBAC) tokens
100% private client side execution with zero network transmission
Frequently Asked Questions
Are my confidential JWT tokens sent to your servers?
No. The entire decoding and signature verification engine runs 100% in your local web browser memory using JavaScript and Web Crypto APIs. No tokens, keys, or claims are ever transmitted over the network.
What is a JSON Web Token (JWT)?
A JWT is an open RFC 7519 standard that defines a compact, URL-safe means for securely transmitting information between parties as a JSON object, digitally signed with HMAC, RSA, or ECDSA.
Can this tool verify RS256 or ES256 signatures?
Currently in-browser verification supports HS256 shared secret signatures. RS256 and ES256 public key verification can be inspected by decoding the public claims.
What does "alg": "none" mean?
"alg": "none" indicates that the token has no digital signature, meaning anyone could modify its claims without detection. It is considered an insecure vulnerability in production environments.