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Secure JWT Decoder

Decode, inspect, and verify JSON Web Tokens instantly. Built for developers with strict local-only processing to prevent token leakage.

Encoded Token
Paste a JWT here to decode...

100% Local Processing. Your token is decoded using your browser's native Base64 decoder. It is never sent over a network or saved to a server.

Header Algorithm & Token Type 
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Payload Data & Claims 
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Signature Verification

Free Online JWT Decoder & Verifier

The ZrirJaouad JWT Decoder is an essential tool for software engineers, backend developers, and cybersecurity professionals. JSON Web Tokens (JWT) are the modern standard for securely transmitting authentication claims between parties (such as an API and a React frontend). However, because JWTs are base64-encoded, you cannot read the payload without decoding it first. The danger is that pasting production tokens into standard online decoders puts your system at risk if the website logs your data. Our tool utilizes strict Zero-Trust Client-Side Architecture. The decoding and signature verification algorithms run 100% locally in your web browser's memory, ensuring your sensitive auth tokens never touch a remote server.

Understanding the Structure of a JWT

A JSON Web Token consists of three distinct parts separated by dots (.). Our visualizer color-codes these sections for easy reading:

  • 1. The Header:
    The first part of the token typically consists of two parts: the type of the token (which is JWT), and the signing algorithm being used, such as HMAC SHA256 (HS256) or RSA (RS256).
  • 2. The Payload (Claims):
    The middle section contains the claims. Claims are statements about an entity (typically, the user) and additional data. Common standard claims include sub (subject/user ID), iat (issued at timestamp), and exp (expiration timestamp). Our tool automatically detects Unix timestamps and translates them into human-readable local dates.
  • 3. The Signature:
    To create the signature part, the server takes the encoded header, the encoded payload, a secret key, and signs that using the algorithm specified in the header. The signature is 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.

Frequently Asked Questions (FAQ)

Is a JWT encrypted or encoded?

Standard JWTs are encoded (specifically Base64Url encoded), NOT encrypted. This means anyone who gets their hands on the token can easily decode it and read the payload. You should never put secret information (like passwords or credit card numbers) in a standard JWT payload. The security of a JWT relies on the signature, which prevents malicious users from altering the payload.

How does the local Signature Verification work?

If your token uses the standard HS256 algorithm, you can paste your backend Secret Key into the verification box. Our tool uses the browser's native Web Crypto API to mathematically hash the header and payload with your secret key. If the resulting hash matches the signature attached to the token, the token is verified as authentic and untampered.

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