Online JWT Decoder
Decode and inspect JSON Web Tokens (JWT) headers, payloads, and claims instantly inside your browser with complete privacy.
Comprehensive Guide to JSON Web Tokens (JWT)
A JSON Web Token (JWT) is an open, industry-standard RFC 7519 method for securely representing claims between two parties. They are widely used in modern web applications, microservices, and REST APIs for stateless authentication and authorization. Because JWTs are compactly and self-containedly structured, developers frequently need to inspect their internal headers and payloads during debugging and security audits.
Anatomy of a JWT Structure
A standard encoded JSON Web Token consists of three base64url-encoded parts separated by dots (.):
- Header: Typically consists of two parts: the token type (JWT) and the signing algorithm being used (such as HMAC SHA256 or RSA).
- Payload: Contains the claims. Claims are statements about an entity (typically, the user) and additional metadata such as expiration time (
exp), issued at (iat), and subject (sub). - Signature: Used to verify that the sender of the token is who it says they are and to ensure that the message wasn’t tampered with along the way.
Why Use a Client-Side JWT Decoder?
When debugging authentication tokens or inspecting API responses, privacy is critical. Sending production authentication tokens or session claims to unverified third-party servers presents a security risk. This tool executes entirely client-side using JavaScript, meaning your tokens never leave your browser.
Frequently Asked Questions (FAQ)
Does this tool verify the cryptographic signature?
This utility decodes and inspects the token components for readability. While it displays the base64 signature string, full cryptographic verification requires your server’s secret key or public certificate.
Are my tokens stored or logged?
No. All parsing runs locally inside your browser’s memory and is discarded when you close or refresh the page.