Verify JWT RS256 / RS512 Signature Online Free

JSON Web Tokens signed with RS256 or RS512 use an RSA private key to sign and a public key to verify — and checking that signature can be tricky without the right tool. This free JWT RS256/RS512 verifier lets you paste any token and its corresponding RSA public key to instantly confirm the signature is valid, all without sending your data anywhere. Everything runs directly in your browser, so your tokens and keys stay completely private.

How to Verify a JWT RS256 or RS512 Signature

1. Paste your JWT into the token field. The tool will automatically decode the header and payload so you can see them before verifying.
2. Paste your RSA public key (PEM format) into the public key field. This is the key that matches the private key used to sign the token.
3. Click "Verify Signature." The tool will check the signature against the key and display a clear pass or fail result in under a second.
4. Review the decoded payload — expiration (exp), issued-at (iat), audience (aud), and all other claims are displayed in readable JSON.
5. Check expiration status — the tool automatically flags whether the token is expired based on the exp claim.

Why Use Flipper File to Verify JWT RS256 Signatures?

• 100% client-side processing — your token and private key never leave your browser. Nothing is sent to any server.
• Supports both RS256 and RS512 — the algorithm is read directly from the JWT header so you don't have to choose manually.
• Full payload decode — see every claim in the token header and body, formatted as readable JSON.
• Expiration check included — instantly see if a token is expired, active, or not-yet-valid based on exp and nbf claims.
• PEM key format support — paste your public key in standard PEM format (-----BEGIN PUBLIC KEY-----); the tool handles parsing.
• No login, no limits — verify as many tokens as you need with no account required and no rate limits.

Frequently Asked Questions

What is RS256 and how is it different from HS256?

RS256 (RSA Signature with SHA-256) uses an asymmetric key pair — a private key signs the token, and a public key verifies it. HS256 uses a single shared secret for both signing and verification. RS256 is preferred in distributed systems where you want to share the ability to verify tokens without sharing the signing secret.

What format does the public key need to be in?

The tool accepts RSA public keys in standard PEM format, which looks like -----BEGIN PUBLIC KEY----- followed by base64-encoded data and -----END PUBLIC KEY-----. Most JWT libraries and cloud identity providers export keys in this format.

Does this tool support RS512?

Yes. The algorithm (alg claim) is read automatically from the JWT header. If your token was signed with RS512, the tool will use SHA-512 for the signature hash automatically. You do not need to select the algorithm manually.

Will my JWT or public key be sent to any server?

No. This tool runs entirely in your browser using the Web Crypto API. Your token, payload, and public key never leave your device.

What happens if the signature verification fails?

The tool will display a clear "Signature Invalid" result in red. Common reasons include: using the wrong public key, a token that was tampered with, or a key/algorithm mismatch (e.g., trying to verify an RS256 token with an EC key).

Can I use this to verify tokens from Auth0, Firebase, or AWS Cognito?

Yes. These providers use RS256-signed JWTs. You can find their public keys in their JWKS (JSON Web Key Set) endpoints, convert a JWK to PEM using a tool, then paste the PEM key here to verify.

What is the difference between RS256 and RS512?

Both use RSA asymmetric keys. RS256 uses SHA-256 to hash the signing input; RS512 uses SHA-512. RS512 produces a longer, more collision-resistant signature but is marginally slower to compute. Most modern systems use RS256.

Can I decode a JWT without verifying the signature?

Yes — the tool will decode and display the header and payload claims as soon as you paste a valid JWT, even before you provide a public key. The signature verification is a separate step.