Guide
JWT Decoder — complete guide
What is a JWT Decoder?
JSON Web Tokens (JWTs) are compact tokens with three Base64URL segments: header, payload, and signature. A JWT decoder shows the header and payload as readable JSON so you can inspect claims like sub, exp, iss, and custom app fields.
The JWT Decoder on space4.dev never sends your token to a server. That is important because access tokens often unlock user sessions — uploading them to a random website is a security risk.
How to decode a JWT safely
Recommended steps:
- Copy the token from your Authorization header or cookie (only from environments you control).
- Paste it into the JWT Decoder on this page.
- Inspect the header (alg, typ, kid) and payload claims.
- Check exp / nbf with the JWT Expiry Checker if you need time validation.
- Do not paste production tokens into untrusted third-party sites that upload data.
What this decoder does not do
Decoding is not the same as verifying a signature. Verifying requires the issuer’s secret or public key. This tool helps you read claims during debugging; it does not prove the token is authentic. Always verify JWTs on your server before trusting them.