JWT Tokens Explained: How They Work and When to Use Them

JSON Web Tokens (JWT) are a compact way to transmit information between parties as a JSON object. They are widely used for authentication in modern web applications.

JWT Structure

A JWT consists of three parts separated by dots: header, payload, and signature. The header specifies the algorithm used for signing. The payload contains claims (statements about the user). The signature verifies the token has not been tampered with.

How JWT Authentication Works

The user logs in with credentials. The server creates a JWT with user information and signs it with a secret key. The client stores the token (usually in memory or a cookie) and includes it in subsequent requests. The server verifies the signature on each request.

Common Claims

Standard claims include: iss (issuer), sub (subject), exp (expiration time), iat (issued at), and aud (audience). Custom claims can contain any application-specific data. Use our JWT Decoder to inspect token contents.

Security Considerations

Never store sensitive data in JWT payloads since they are only encoded, not encrypted. Always verify signatures on the server. Set reasonable expiration times. Use HTTPS to prevent token interception. Consider token refresh strategies for long-lived sessions.

JWT vs Session Cookies

JWTs are stateless, meaning the server does not need to store session data. This makes them ideal for distributed systems and microservices. Session cookies require server-side storage but offer simpler revocation.