JWT Debugger - Decode Tokens Offline
Debug your authentication tokens without exposing your secrets to third-party services. This 100% client-side JWT decoder processes tokens entirely in your browser - no network requests, no server uploads, no data leakage. Perfect for developers debugging auth issues, security auditors reviewing tokens, or anyone who needs to inspect JWT claims without compromising credentials. Use JWT Decoder when you need answers fast during debugging, reviews, or incident triage. Paste your input, validate the output, then copy results into tickets or docs in seconds. Most processing runs in your browser, so you can test safely without unnecessary data exposure. Built for speed, clarity, and repeat use.
Header
Algorithm and token type information
Payload
User data and claims (not encrypted - anyone can read this!)
Signature
Cryptographic signature (requires secret key to verify)
Token Status
How to Use This JWT Debugger
- Paste your JWT token into the text field above (the example token is pre-loaded)
- View the decoded Header - Shows the algorithm (HS256, RS256, etc.) and token type
- Inspect the Payload - Contains the claims like user ID, roles, and expiration time
- Check the Signature - The cryptographic signature that verifies authenticity
- Review Token Status - Instantly see if your token has expired
Why Use a Client-Side JWT Decoder?
JWTs contain sensitive information: user IDs, roles, permissions, and session data. Pasting tokens into online tools like jwt.io sends them to external servers, creating security risks. This decoder uses JavaScript's built-in atob() function to parse Base64URL-encoded segments entirely in your browser's memory.
How JWT Structure Works: A JWT consists of three Base64URL-encoded parts separated by dots: header.payload.signature. The header specifies the algorithm, the payload contains claims, and the signature verifies integrity. While the header and payload are only encoded (not encrypted), the signature requires the secret key to verify - which this tool cannot do without compromising your security.
Security Note: Remember that anyone with a JWT can decode and read the payload. Never store sensitive data in JWT claims. JWTs are for authentication claims that can be verified, not for secrets that must remain hidden.