JWT Debugger Online
Debugging a JWT problem usually means answering three questions: What algorithm was used? Have any claims changed? Is the signature valid? This tool answers all three in one place, entirely in your browser.
Paste the token to instantly see the decoded header (algorithm, key ID, token type) and payload (all claims, formatted). Standard registered claims (exp, nbf, iat) are displayed with human-readable dates and a clear EXPIRED label when past expiry. For signature verification enter your HMAC secret or PEM public key — HS256/384/512, RS256/384/512, and ES256/384/512 are all supported via the Web Crypto API.
Unlike jwt.io or other online debuggers, nothing is sent to a server. Use it freely with production tokens, tokens containing PII, or tokens that include API credentials.
How to use
- Paste your JWT token into the input field on the main tool page.
- The header and payload are decoded instantly — review claims, algorithm, and expiry.
- To verify the signature, paste your HMAC secret or PEM public key and click Verify Signature.