JWT Signature Verifier
Verify whether an HS256 JWT signature matches the token header and payload for the shared secret you enter.
Verification Result
Security Note
Verification happens locally inside your browser. Avoid using live production tokens or secrets unless you understand the risk. A valid signature confirms integrity for the supplied secret, not that the claims are acceptable or the token should be trusted.
Verifying JWT Signatures Before Trusting Tokens
HS256 uses one shared secret to create and verify an HMAC-SHA256 signature. Verification checks whether the encoded header and payload match the signature for the secret you provide.
This tool reads the algorithm declared in the JWT header and only proceeds when it is exactly HS256. Tokens using RS256, ES256, none, or another algorithm require a different verification method.
A successful signature check does not validate exp, nbf, iss, aud, permissions, revocation, or application policy. Those checks must be performed separately.
How to Use the JWT Signature Verifier
- Paste your JWT token into the editor.
- Enter the secret key used to sign the token.
- Click Verify JWT Signature.
- Review the result, then validate the token claims and application rules separately.
Common Use Cases
- Testing JWT authentication systems.
- Debugging invalid token signature errors.
- Inspecting HS256-signed JWT tokens.
- Verifying API authentication workflows.
- Checking token integrity during development.
- Testing session and authorization systems.
- Debugging OAuth and backend authentication flows.
Understanding JWT Signature Verification
- Header: Contains token metadata and signing algorithm details.
- Payload: Contains claims, permissions, and token information.
- Signature: Confirms whether the token was signed using the correct secret key.
- Verification: Helps detect modified or invalid tokens during authentication workflows.
Example Verification Workflow
1. Paste JWT token 2. Enter secret key 3. Verify signature 4. Review claims and application rules separately
Frequently Asked Questions
What is JWT signature verification?
It checks whether the JWT signature matches the encoded header and payload for the shared HS256 secret you entered.
Which JWT algorithm does this tool support?
This verifier currently supports HS256 JWT signature verification using HMAC SHA-256.
Does this tool decode JWT payloads?
This tool focuses on signature verification. You can use the JWT Decoder tool to inspect payload data separately.
Are JWT secrets uploaded anywhere?
No. Verification happens locally inside your browser and secrets are not uploaded or stored.
Why would JWT verification fail?
Verification can fail because of invalid signatures, incorrect secrets, modified payloads, unsupported algorithms, or malformed tokens.