What is the 'exp' claim in a JWT?

The 'exp' (expiration time) claim identifies the expiration timestamp on or after which the JWT must not be accepted for authentication processing.

Updated: August 2026 • Verified v1.2

JWT Payload Inspector & Client-Side HMAC Validator

Developer ToolsHigh Usage

Local Browser Execution: Your input is processed locally in your browser and is not sent to UTL servers.

Web Crypto HMAC-SHA256: Signature = HMAC_SHA256(Base64URL(Header) + '.' + Base64URL(Payload), Secret)

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Understanding Your Results

Decodes JSON Web Tokens locally, formats header and payload claims, computes real-time expiration timelines, and verifies HS256 signatures using the browser Web Crypto API.

Practical Guidance & Next Steps

Never paste production JWT secrets or user tokens into untrusted third-party online decoders. This tool executes 100% client-side.

What is this?

A zero-knowledge developer utility that decodes JWTs, checks expiration claims, and validates HMAC-SHA256 signatures in browser memory.

How does it work?

1. Paste your encoded JWT. 2. View decoded header and payload claims with live expiration status. 3. Enter your secret key to verify HMAC-SHA256 signature integrity locally.

Why use it?

Protects sensitive user authentication tokens and JWT secrets from third-party server logging.

Technical Scope & Calculation Limitations

Supports HS256 (HMAC-SHA256) signature verification via native Web Crypto API.

Frequently Asked Questions

Yes. Unlike many web decoders, this utility runs 100% inside your local web browser using native JavaScript and Web Crypto APIs with zero network requests.

Windows Desktop & Widget Options