JWT Validator
Validate JWT structure, expiry claims, and optional HMAC signatures.
The JWT Validator is an indispensable online utility for developers and security professionals working with JSON Web Tokens. This tool provides a comprehensive way to inspect, decode, and validate the integrity of any JWT string you encounter. Whether you're debugging a stubborn API authentication error, verifying tokens generated by your own application, or scrutinizing tokens received from third-party services, this validator offers immediate insights.
Simply paste your JWT into the input field, and the tool instantly breaks down its three base64-encoded parts: the header, the payload, and the signature. It checks the structural validity, ensuring all parts are correctly formatted. Crucially, the JWT Validator goes further by analyzing standard claims within the payload, such as exp (expiration time), nbf (not before time), and iat (issued at time), alerting you to any expired or prematurely used tokens.
A key feature is its ability to validate HMAC signatures. If your JWT uses an HS256, HS384, or HS512 algorithm, you can provide the secret key to verify the token's authenticity, ensuring it hasn't been tampered with since it was issued. The typical output includes the decoded header and payload, a clear "Valid" or "Invalid" status, and detailed error messages if validation fails (e.g., "Token expired," "Invalid signature").
A useful tip: while the validator excels at HMAC signature verification, remember that it currently does not support asymmetric key algorithms like RSA or ECDSA. For those, you'd need a different tool or library. Use the JWT Validator to streamline your development workflow and enhance your understanding of token-based authentication systems.
How to use JWT Validator
Paste Your JWT
Copy the JSON Web Token string you wish to validate and paste it into the designated input area of the JWT Validator tool.
Review Decoded Parts
The tool will immediately decode the header and payload sections, displaying their human-readable JSON content for inspection.
Check Validation Status
Observe the prominent status indicator which will tell you if the JWT is structurally valid and if any standard claims like exp or nbf are met.
Verify HMAC Signature (Optional)
If your JWT uses an HMAC algorithm (e.g., HS256) and you have the secret key, enter it into the "Secret Key" field to check the token's cryptographic integrity against tampering.
Interpret Error Messages
If the token is invalid, review the detailed error messages provided to understand specific issues such as expiry, malformation, or an incorrect signature.
Frequently Asked Questions
What types of JWT claims does the validator check?
The JWT Validator specifically checks standard claims like exp (expiration time), nbf (not before time), and iat (issued at time). It will alert you if a token is expired or used prematurely.
Can I validate JWTs with asymmetric signatures (e.g., RSA, ECDSA)?
Currently, the JWT Validator supports HMAC-based signatures (HS256, HS384, HS512) where a shared secret is used. It does not perform validation for asymmetric signatures like RSA or ECDSA.
What does an "Invalid Signature" error mean?
An "Invalid Signature" error typically indicates one of two things: either the secret key you provided for HMAC validation is incorrect, or the token's header or payload has been tampered with after it was issued.
Does the JWT Validator store my tokens or secret keys?
No, the JWT Validator is designed to operate entirely client-side in your browser. Neither your tokens nor your secret keys are transmitted to any server or stored, ensuring your data remains private.
How does this tool help me debug API authentication issues?
By quickly decoding and validating tokens, you can identify if an API is rejecting a token due to expiry, an invalid structure, or a tampered signature, allowing you to pinpoint the root cause of authentication failures faster.
Is there a limit to the length of the JWT I can validate?
While there isn't a strict character limit enforced by the tool itself, extremely long JWTs (e.g., many kilobytes) might experience slight performance delays in your browser, but the functionality remains the same.