JWT ValidatorValidate JWT tokens — verify HMAC signature, check expiration, inspect claims.
JWT Validator
Validate JWT tokens — verify HMAC signature, check expiration, inspect claims.
Paste Token
Paste JWT to validate.
Enter Secret
Enter HMAC secret for signature check.
Validate
Check signature and expiry.
What Is JWT Validator?
Validates JWTs by verifying HMAC signature and checking expiration. Paste a JWT and provide the signing secret to verify integrity. The tool decodes header/payload, checks exp claim, and recomputes the HMAC signature for comparison. Supports HS256, HS384, HS512 via Web Crypto API. Essential for debugging auth issues and verifying token integrity. Without a secret, only structure and expiration are checked. All processing is client-side.
Why Use Our JWT Validator?
- Verifies HMAC signatures (HS256/384/512)
- Checks expiration automatically
- Decodes and displays all claims
- 100% client-side — secrets never transmitted
Common Use Cases
Security Audit
Verify JWT integrity.
Debugging
Diagnose auth failures.
Testing
Verify app-generated tokens.
Compliance
Ensure token security.
Technical Guide
JWT validation: (1) Split token into 3 parts. (2) Decode header for algorithm. (3) Recompute HMAC over header.payload with secret. (4) Compare signatures. (5) Check exp vs current time. Uses subtle.sign() to recompute. Supports HS256/384/512.
Tips & Best Practices
- 1Signature needs original secret
- 2Without secret, structure/expiration only
- 3Valid signature = no tampering
- 4Check both signature AND expiration
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Encoding & CryptoFrequently Asked Questions
QFree?
QSecret safe?
QWithout secret?
QAlgorithms?
QDetect expired?
About JWT Validator
JWT Validator is a free online tool from FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration required. No ads. Just fast, reliable tools.