What JWT Tokens Are and Why Modern Apps Rely on Them for Authentication

JWT (JSON Web Token) is a compact, self-contained string used to carry user identity and permissions in modern applications without repeated server-side lookups. Unlike traditional server-side sessions, which require storing and retrieving session data on every request, JWTs embed identity information directly in a tamper-proof token issued to the client. A JWT consists of three dot-separated parts — a header, a payload containing user claims, and a cryptographic signature — making it independently verifiable by any system. The payload is Base64-encoded rather than encrypted, meaning its contents are readable by anyone who holds the token, so sensitive data should never be stored inside it. As applications became more distributed and API-driven, JWTs emerged as the standard authentication mechanism due to their stateless, scalable nature.