JWT Decoder

Decode JWT (JSON Web Token) to view header and payload contents. Easily check token expiration, issuer, and other claim information.

Enter JWT Token

Key Features

Header Analysis

Check algorithm, token type and more

Payload Viewer

View user info, permissions and claims

Expiration Check

Verify token validity and expiration

Privacy First

All processing in browser, no server upload

Notice

Signature verification is not performed (requires secret key).
Handle tokens with sensitive information carefully.
All processing happens in your browser only.

Frequently Asked Questions

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties. It contains information encoded as a JSON object and can be verified with a digital signature. It is primarily used for authentication and information exchange.

A JWT consists of three parts separated by dots (.): Header, Payload, and Signature. The header contains the token type and signing algorithm, the payload contains claims (such as user information), and the signature is a verification value to prevent tampering. Each part is Base64URL encoded.

A JWT signature is generated by hashing the header and payload with a secret key (HMAC) or private key (RSA/ECDSA). The recipient verifies integrity by regenerating the signature with the same key and comparing. This decoder does not perform signature verification (no secret key), but you can inspect the token contents.

JWT payloads are only Base64 encoded, not encrypted, so they must not contain sensitive data (passwords, personal information, etc.). Always set a token expiration time (exp) and transmit tokens over HTTPS only. Secret keys should be sufficiently complex and stored securely.

How JWT Authentication Works and Its Role in Web Development

JWT-Based Authentication Flow

When a user logs in, the server generates a JWT containing user information and sends it to the client. For subsequent API requests, the client includes the JWT in the Authorization header as a Bearer token. The server validates the token using the secret key, maintaining state without needing a separate session store.

Session Authentication vs. JWT Authentication

Traditional session authentication stores session data on the server and sends only a session ID to the client via cookie. JWT places all information inside the token itself, enabling stateless operation where the server stores nothing. JWT is especially advantageous for microservices, mobile apps, and SPAs, and scales horizontally with ease.

JWT in Real-World Applications

The dual-token strategy using both an Access Token and a Refresh Token is widely adopted. The Access Token is set with a short expiry (15 minutes to 1 hour), and a new Access Token is obtained using the Refresh Token. Modern authentication protocols such as OAuth 2.0 and OpenID Connect are also commonly implemented using JWT.

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