JWT Decoder: How to Decode and Debug JWT Tokens

JSON Web Tokens (JWT) are everywhere in modern authentication. Learn how to decode JWT tokens to debug authentication issues.

What is a JWT?

A JWT consists of three parts: Header, Payload, and Signature - separated by dots.

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

How to Decode a JWT

1. Paste your JWT token
2. Click "Process"
3. View the decoded header and payload

Common JWT Claims

• sub (Subject) - User identifier
• exp (Expiration) - Token expiry time
• iat (Issued At) - Token creation time
• iss (Issuer) - Who created the token

Check Token Expiration

Our decoder shows the expiration timestamp, human-readable date/time, and whether the token is still valid.

Debugging Authentication Issues

When debugging auth problems:

1. Decode the JWT to check expiration
2. Verify the payload contains expected claims
3. Check the JSON structure of the payload
4. If using Basic Auth, also check Base64 encoding

JWT vs Base64

JWTs use Base64URL encoding (a variant of Base64), but they're not the same:

• Base64 is just encoding
• JWT includes structure and (usually) cryptographic signing

Security Note

Our tool runs entirely in your browser - nothing is sent to any server. Safe for debugging sensitive tokens.

Related Developer Tools

• JSON Formatter - Format the decoded payload
• Base64 Encoder - Understand token encoding
• Regex Tester - Extract tokens from logs

Conclusion

Debugging JWT issues is easy with our free decoder. Paste any JWT to instantly view its contents and check expiration.