How to Use the JWT Decoder Tool
Learn the principles of JSON Web Tokens and how to safely inspect payloads in your browser.
Introduction
A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information. Our tool lets you decode and audit these tokens instantly and privately.
Step-by-Step Guide
Paste Your Token
Copy your encoded JWT and paste it into the input area. The tool will automatically detect the header, payload, and signature segments.
Inspect the Header
Review the metadata, including the algorithm (e.g., HS256) and the token type. This is critical for preventing "alg: none" attacks.
Audit the Payload
Examine the decoded claims like `exp` (expiry), `sub` (subject), and `iat` (issued at). Verify that your backend is injecting the correct user roles.
Pro Tips & Best Practices
Always verify the "exp" claim to troubleshoot authentication timeouts.
Use the tool to check for sensitive data (PII) accidentally stored in the payload.
Keep your browser console open while debugging for additional low-level metadata.
Common Mistakes to Avoid
Frequently Asked Questions
Is it safe to decode tokens here?
Yes. All decoding happens 100% locally in your browser. No token data is ever sent to or stored on our servers.
Can I verify the signature?
Verification requires your secret key. For security, we recommend only performing verification on your own trusted server environment.