Client-Side JWT Decoder & Expiry Checker - 100% Private
Decode JSON Web Tokens, inspect Header & Payload claims, monitor real-time expiration countdowns, and verify signatures locally without exposing secrets.
100% Zero-Upload Security: Never paste tokens into cloud tools. All parsing and signature checks run locally on your device.
All file encoding, rendering, and transformations run inside local browser memory.
Key Features & Performance Capabilities
Visual Color-Coded Split
Instantly distinguish the three token components: Red for Header, Purple for Payload claims, and Sky Blue for cryptographic Signature.
Live Expiration Countdown Timer
Monitors the 'exp' claim with a real-time relative countdown timer ('Expires in 2h 15m' or 'Expired 3d ago') and local timestamp conversion.
HMAC Signature Verification
Verify HS256, HS384, and HS512 signatures locally using the native Web Crypto API with text or Base64 secret keys.
Zero Token Logging
Guarantees complete token confidentiality: your production tokens, user claims, and authorization scopes never leave your browser.
How to Use JWT Decoder & Expiry Checker
Paste JWT Token
Paste your encoded JSON Web Token into the input area, or click 'Load Valid Sample' to test the interface.
Inspect Decoded Claims
Review the parsed Header (algorithm, token type) and Payload claims (subject, issuer, audience, custom roles).
Check Expiration Status
Check the live expiration status card to verify whether the token is currently active or expired.
Optionally Verify Signature
Enter your secret key in the verification panel and click 'Check Signature' to validate cryptographic authenticity.
How JSON Web Tokens Work & Why Client-Side Debugging is Essential
The Architecture of a JSON Web Token
A JSON Web Token (JWT, RFC 7519) consists of three dot-separated components: Header, Payload, and Signature. The Header specifies the signing algorithm (e.g. HS256, RS256). The Payload contains authorization claims, identity data, and timestamp metadata (iat, exp, nbf). The Signature is generated by hashing the encoded Header and Payload with a secret or private key.
The Severe Security Risk of Cloud JWT Inspectors
Past software tokens into third-party cloud debuggers exposes active session tokens, admin credentials, and cryptographic signing keys to third-party logging and potential interception. VicanTools performs all decoding and cryptographic HMAC verification directly within your local browser, eliminating data breach risks.
Frequently Asked Questions (FAQ)
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