What is the JWT Decoder?
A JSON Web Token (JWT) is a compact, URL-safe means of representing claims transferred between two parties. The decoder parses the Base64Url encoded segments to reveal the Header, Payload, and Signature.
Key Features
Decode Base64Url JWTs
View Header Algorithms
Inspect Payload Claims
Verify Signature Structure
100% Client-Side parsing
How to use the JWT Decoder
- Paste your JWT string (starting with 'ey') into the input field.
- The tool instantly splits the token into its three distinct parts.
- Review the decoded JSON Header and Payload in the right pane.
Examples
Input
eyJhbGciOiJIUzI1NiIsInR5cCI... (Truncated JWT)
Output
Header: { "alg": "HS256", "typ": "JWT" }
Payload: { "userId": 123, "admin": true } Common Errors & Troubleshooting
Malformed Token
A valid JWT must have exactly three parts separated by dots (.).
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 (Missing payload/signature)
When should you use this tool?
- Debugging authentication flows.
- Inspecting user claims and roles embedded in a token.
- Verifying token expiration dates (exp claims).
What's the difference?
JWT Decoder
Reads the contents of the token so developers can inspect the payload.
JWT Verifier
Cryptographically ensures the token hasn't been tampered with using a secret key.
Tool Comparison
| Feature | ByteUtils |
|---|---|
| Decode Header | |
| Decode Payload | |
| Requires Secret Key | No |
| No Server Uploads |
Frequently Asked Questions
Is it safe to decode JWTs online?
Yes, provided the tool is purely client-side like this one.
Can I modify and re-sign the JWT?
No. You need the original secret key to re-sign a token.
Are JWT payloads encrypted?
No. Standard JWT payloads are merely Base64 encoded.
Privacy First
All processing happens directly in your browser. Your data, payloads, and files are never uploaded to our servers or tracked.
Tool Information
- Category: security
- Runs in Browser: Yes
- Requires Login: No
- Mobile Friendly: Yes