JSON Web Token (JWT) Meaning

A compact, URL-safe means of representing "claims" to be transferred between two parties. It is a standard for securely transmitting information as a JSON object.

JWTs are most commonly used for "authentication"-after a user logs in, the server gives them a JWT that they use for all future requests to prove who they are. A JWT consists of three parts: a header, a payload (the data), and a signature.

The signature is the most important part; it is created using a "secret key" known only to the server. If an attacker tries to change the data in the JWT (e.g., trying to change their "user_id" to "admin"), the signature will no longer match, and the server will reject the token.

JWTs are the "passport" of the modern web. Because they are stateless-meaning the server doesn't have to remember every active session in a database-they allow for highly scalable applications.

They are widely used in the APIs that connect mobile wallets to centralized exchanges and fintech services.