Introduction

What is a JWT Decoder?

A JWT (JSON Web Token) decoder is an essential developer tool used to parse, inspect, and validate authentication tokens. JWTs are widely used in modern web applications to securely transmit information between a client and a server. Our free JWT Decoder allows you to instantly unpack the token into its three core components: the Header, the Payload, and the Signature.

Why You Need to Validate JWTs

When debugging API authentication, OAuth flows, or single sign-on (SSO) integrations, developers often need to check the claims embedded inside a JWT. By pasting your token into our tool, you can verify critical information such as:

• Expiration timestamps (exp)
• Issued at times (iat)
• Subject identities (sub)
• Issuer URLs (iss)

Security First: Client-Side Processing

Unlike many online developer tools that silently log your inputs, our JWT Decoder is built with privacy-first architecture. All decoding, base64url parsing, and formatting is executed locally inside your browser using JavaScript. Your sensitive access tokens and identity claims never touch a backend server, ensuring your production credentials remain secure.

How It Works

A standard JWT consists of three parts separated by dots (.):

1. Header: Contains metadata about the token, such as the algorithm used (e.g., HS256, RS256).
2. Payload: Contains the claims, which are statements about an entity (typically, the user) and additional data.
3. Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.

// Header
{
  "alg": "HS256",
  "typ": "JWT"
}
// Payload
{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022
}