JWT Decoder

No, JWT is not an authentication protocol—it's a token format. OAuth 2.0 and OpenID Connect are authentication and authorization protocols that often use JWTs as the token format. JWT simply provides a standardized way to represent claims in a compact, URL-safe format. You can use JWTs with various authentication mechanisms including session-based auth, bearer tokens, or OAuth flows.

No, decoding and verifying are two different operations. Decoding simply reads the Base64URL-encoded header and payload to view their contents—anyone can decode a JWT without any secret or key. Verification, on the other hand, checks the signature using the appropriate key to ensure the token hasn't been tampered with and was issued by a trusted party. Our tool only decodes JWTs; it does not verify signatures.

Yes. All JWT decoding happens entirely in your browser using JavaScript. No data is ever transmitted to our servers or any third party. You can verify this by checking your browser's network activity or by disconnecting from the internet after loading the page—the tool will continue to work. However, remember that JWTs are not encrypted by default, only signed. Anyone with access to a JWT can decode and read its contents.

The "none" algorithm means the JWT has no signature and provides no cryptographic protection. While technically valid per the JWT spec, it's extremely dangerous in production because anyone can create or modify these tokens. Attackers can change user IDs, permissions, or expiration dates without detection. Some libraries have been vulnerable to accepting "none" algorithm tokens even when expecting signed tokens. Always use proper signing algorithms in production.

JWT lifetime depends on your security requirements and use case. Access tokens should be short-lived (5-15 minutes) to limit the window of opportunity if compromised. Refresh tokens can last longer (days to weeks) but should be securely stored and rotated. For highly sensitive operations, use even shorter expiration times. Always implement the "exp" (expiration) claim and validate it on the server side. Consider implementing token refresh mechanisms to maintain user sessions without requiring frequent re-authentication.

Generally, no. JWTs are Base64URL-encoded, not encrypted—anyone who obtains the token can decode and read its contents. Only include information necessary for authorization decisions (user ID, roles, permissions) and avoid sensitive data like passwords, social security numbers, or credit card details. If you must include sensitive data, use JWE (JSON Web Encryption) to encrypt the entire token, or encrypt specific claims before including them in the JWT.

JWT (JSON Web Token) is signed but not encrypted—the header and payload are readable by anyone. JWE (JSON Web Encryption) encrypts the entire content, making it unreadable without the decryption key. JWTs are sufficient when you only need to verify authenticity and integrity. Use JWE when the claims themselves are sensitive and must be kept confidential. JWE tokens are typically longer and require more computational resources to process than JWTs.

JWTs are stateless and self-contained, so they cannot be inherently revoked. Once issued, a JWT remains valid until it expires. However, you can implement revocation through several strategies: maintain a blacklist of revoked tokens, use short expiration times with refresh tokens, include a unique token ID (jti) and check it against a database on each request, or implement token versioning where changing a user's token version invalidates all previous tokens. Each approach has trade-offs between security and performance.

Symmetric algorithms (HS256, HS384, HS512) use the same secret key for both signing and verification. This is faster but requires both the issuer and verifier to securely share the secret. Asymmetric algorithms (RS256, ES256, etc.) use a private key for signing and a public key for verification. The private key remains secret with the token issuer, while the public key can be freely distributed to anyone who needs to verify tokens. Use symmetric for single-application scenarios and asymmetric for distributed systems or third-party verification.

This is a debated topic in web security. Options include: (1) HttpOnly cookies—protected from XSS but vulnerable to CSRF (mitigate with SameSite attribute), (2) localStorage/sessionStorage —vulnerable to XSS but not CSRF, or (3) memory (JavaScript variables)—most secure but lost on page refresh. For SPAs, many developers use HttpOnly cookies with SameSite=Strict or Lax and CSRF tokens. For mobile apps, use secure platform-specific storage. Never store tokens in regular cookies accessible to JavaScript, and always use HTTPS to prevent token interception.