Secure JWT Token Decoder
Decode JSON Web Tokens (JWT) client-side instantly. Extract token headers, payload claims, and check expiry status. Done entirely locally.
Frequently Asked Questions
What is a JSON Web Token (JWT)?
JSON Web Tokens (JWT) are an open, industry-standard RFC 7519 method for representing claims securely between two parties. JWTs are compact, URL-safe, and commonly used for stateless authorization handshakes, Single Sign-On (SSO) headers, and microservice contexts.
Structure of a JWT Token
A JWT is composed of three distinct base64url-encoded parts separated by dots (.):
- Header (Red): Declares the token type (typically
JWT) and the cryptographic signing algorithm in use (e.g.HS256orRS256). - Payload (Blue): Contains the claims. Claims are statements about an entity (typically, the authenticated user) and additional metadata (such as expiration timestamps).
- Signature (Green): Formed by hashing the encoded header, payload, and a secret key using the specified algorithm to ensure that the token was not altered in transit.
JWT Security Warning
It is critical to note that Base64Url encoding is not encryption. A JWT is simply serialized and can be read by anyone who intercepts it. You must never place sensitive information (like user passwords or API credentials keys) in the payload claims. Furthermore, while client-side decoders reveal token values, you must verify signatures cryptographically inside your backend application server using secret keys before trusting their contents.