JWT Decoder, Encoder, and Debugger Online Tool

Instantly decode, validate, and encode JSON Web Tokens (JWTs). View payload claims, check token expiry, and debug authentication flows. Fast, secure, and processing is 100% client-side.

Header (JSON)
Algorithm (`alg`), Token Type (`typ`).
Payload (JSON)
Your custom claims like `sub`, `name`, `iat`, `exp`.
Signature Secret Client-Side Demo
Warning: Entering a secret here is for *demonstration/visuals only*. For production, secrets must be kept server-side!
Used for signature calculation/verification if you implement client-side hashing.
Encoded JWT
Signature (Base64Url Encoded)

...

This is the third part of the JWT. For client-side encoding, this is a placeholder. For decoding, it's extracted from the token.

About This JWT Encoder and Decoder

A **JSON Web Token (JWT)** is a compact, URL-safe means of representing claims to be transferred between two parties. This tool provides a comprehensive, user-friendly interface for developers to interact with JWTs.

Features:

  • **Real-time Encoding:** Type your Header and Payload JSON, and see the first two parts of the JWT generated instantly.
  • **Instant Decoding & Validation:** Paste any JWT into the "Encoded JWT" box to immediately decode its Header and Payload.
  • **Client-Side Processing:** All encoding and decoding operations happen directly in your browser using JavaScript. **No token data or secret keys are ever sent to our servers**, ensuring maximum privacy and security for your sensitive information.
  • **Expiry Status:** The tool automatically checks and displays the validity of the `exp` (expiration) claim, if present, informing you if a token is expired.
  • **Copy to Clipboard:** Easily copy any section (Header, Payload, Encoded JWT, Signature) with dedicated buttons.

How it Works (Client-Side Limitations):

This tool efficiently handles the Base64Url encoding/decoding of the JWT Header and Payload. However, it's crucial to understand:

  • Signature Generation: The signature of a JWT requires a secret key (or private key for asymmetric algorithms) to be securely stored and used. Since this is a client-side tool, **it cannot securely generate or verify the JWT signature using a real secret key.** Any secret key you enter here is for local demonstration purposes only and should *never* be your actual production secret.
  • Server-Side Importance: For real-world applications, JWT signing and verification must always be performed on a secure server where your secret keys can be protected.