JWT Debugger & Decoder: Verify and Inspect JSON Web Tokens Locally
In this guide:
What is a JSON Web Token (JWT)?
JSON Web Tokens (JWT) are an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.
A typical JWT contains three parts separated by dots: Header, Payload, and Signature. Because these segments are Base64Url encoded, they look like a random block of text until they are decoded.
Inspect JWT Header & Claims Instantly
Our local JWT Debugger decodes any standard token instantly, rendering structured, editable fields in raw JSON formatting:
- Header—Decodes details about the algorithm used (e.g. HS256, RS256) and the type of token.
- Payload Claims—Decodes the statement details containing data claims like Subject (sub), Issuer (iss), Issue Time (iat), and Expiry Time (exp). Also maps any custom variables added by authentication libraries (like Auth0, Firebase, or custom backends).
- Signature—Inspects the cryptographic signature block at the tail of the token.
- Claims Status Alerts—Displays expiration indicators, warnings, and local time conversions.
100% Client-Side Privacy Protection
Security is key when analyzing authentication tokens, as payload strings often contain sensitive user emails, account IDs, security roles, and scopes.
ZeroWebTools guarantees that all decoding operations execute directly in your browser's JavaScript engine on your device. No tokens or payloads are ever uploaded to a server, keeping your session credentials entirely secure.
Was this utility tool helpful?
Your anonymous feedback helps us refine our tools and resources.