How does the JWT Debugger & Token Inspector (jwt.io Alternative) work?

100% private, client-side JWT debugger and decoder. Inspect headers, payload claims, and verify HMAC SHA-256 signatures in-browser without sending tokens to remote servers. All processing takes place locally inside your web browser with 100% mathematical precision.

Is this tool free and private?

Yes, this tool is 100% free with no registration, no watermarks, and zero server uploads. Your data never leaves your device.

Can I use this tool on mobile devices?

Yes, JWT Debugger & Token Inspector (jwt.io Alternative) is fully responsive and optimized for all modern Android, iOS, tablet, and desktop web browsers.

100% IN-BROWSER · ZERO SERVER LOGGING

JWT Debugger & Token Inspector

Decode, inspect claims, format JSON payloads, and verify HMAC SHA-256 signatures in real-time. Unlike jwt.io, zero secret keys or auth tokens ever touch a remote server.

Preset Tokens:

🔒 Security Warning: JWTs often contain secret keys and credentials. Pasted tokens run 100% locally in browser memory and are never logged, stored, or sent across the network.

Encoded Token Paste your JWT here

Header Payload Signature

HEADER: ALGORITHM & TOKEN TYPE HS256

PAYLOAD: DATA / CLAIMS

Active Claim

VERIFY SIGNATURE (HMAC-SHA256) Verified

Secret Key: Base64 encoded

🔒 Computed via Web Crypto API (crypto.subtle.sign). Your secret key is never sent across the internet.

⚡ Connected Developer Workflows:

💻 Format Payload in JSON Formatter 🔤 Base64 & URL Encoders 🛡️ Generate Token Checksum 🔍 Test Bearer Regex

How JSON Web Tokens (JWT) Work

A JSON Web Token (RFC 7519) is a compact, URL-safe means of representing claims to be transferred between two parties. Tokens consist of three distinct parts separated by dots (.):

1. Header

Typically consists of two parts: the signing algorithm (e.g., HMAC SHA256 or RSA) and the token type (JWT).

2. Payload

Contains the claims statements about an entity (typically the user) and additional metadata like expiration (exp) and issuer (iss).

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.

Frequently Asked Questions

Is it safe to paste private JWTs and secrets here?

Yes. Unlike other web-based decoders, AG World Tools runs 100% inside your browser using the HTML5 Web Crypto API. No token or secret key is ever transmitted over the network or logged in a database.

What is the "alg: none" attack?

The "none" algorithm indicates an unsigned token. If an authentication server incorrectly accepts tokens with alg: none, attackers can forge arbitrary admin claims without possessing the signature secret. Our debugger automatically alerts you if an unsigned token is detected.