Free JWT Signature Verifier

Free online JWT signature verifier. Validate JSON Web Token signatures. Supports HS256/HS384/HS512/RS256 algorithms. Pure frontend, no server. | No Signup, Client-Side · No Server Uploads

Zero Dependencies·Works Offline

Paste a JWT token and secret key to verify the signature.

JWT Token

Signing Algorithm

Secret Key (HMAC)

Verification Result

Header

Payload

JWT Signature Verifier

A free online tool to verify JSON Web Token signatures. Supports HMAC algorithms, auto-decodes Header and Payload, checks token expiration.

Key Features

Signature verification: Validate JWT signature integrity with a secret key
Auto-decode: Parse Header and Payload into readable JSON
Expiration check: Auto-detect exp field for token validity
Multi-algorithm: HS256/HS384/HS512
Secure & local: All processing in your browser

JWT Structure

JWT has three parts: Header (algorithm and type), Payload (claim data), Signature. Each part is Base64URL-encoded and joined with dots.

FAQ

What is JWT?

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties. It consists of Header, Payload, and Signature separated by dots.

How does signature verification work?

Verification recalculates the signature using Header + Payload + secret key, then compares it with the signature in the JWT. If they match, the token is untampered.

Which algorithms are supported?

Currently supports HMAC algorithms: HS256, HS384, HS512. These are symmetric algorithms using the same key for signing and verification.

Are asymmetric algorithms like RS256 supported?

This version supports HMAC symmetric algorithms only. RS256 and other asymmetric algorithms will be added in future versions.

Is my secret key safe?

All operations happen locally in your browser. Keys and tokens are never sent to any server. Avoid using real production keys.

🔐 JWT Signature Verifier