JWT Verifier
Verify JWT signatures using HMAC algorithms. Paste your token, enter the secret, and validate.
JWT Signature Verifier Online
Verify JSON Web Token (JWT) signatures with HMAC secret keys. Free online JWT verification tool for developers. Check token integrity securely.
How It Works
Paste your JWT and enter the secret key or public key used to sign the token. The tool recalculates the signature using the specified algorithm (HS256, HS384, HS512) and compares it with the signature in the token to confirm validity.
Common Use Cases
- Verifying that a JWT hasn't been tampered with during transmission
- Debugging authentication failures caused by mismatched signing keys
- Confirming the algorithm used to sign a production token
- Learning how JWT signature verification works in practice
Frequently Asked Questions
It confirms that the token hasn't been altered since it was signed. If even one character of the payload changes, the signature will fail verification.
Yes, all verification happens locally in your browser. Your secret key is never sent to our servers.
We support HMAC-based algorithms: HS256, HS384, and HS512.
The tool supports HMAC algorithms (HS256, HS384, HS512) and RSA algorithms (RS256, RS384, RS512). HMAC uses a shared secret; RSA uses a public/private key pair.
If the signature doesn't match, the tool clearly indicates the token is invalid. This means either the token was tampered with, the wrong key was used, or the token is corrupted.
Yes, all verification happens locally in your browser. Your secret key and JWT token are never sent to any server.
HS256 uses a single shared secret (symmetric). RS256 uses a public/private key pair (asymmetric) — the token is signed with a private key and verified with a public key.