SecureDevutils/Security/Client-Side JWT Decoder & Verifier
🔑
JWT Decoder
Decode and inspect JWT tokens including header, payload and signature validation.
JWT
ENCODED HTML / INPUT

JSON Web Token

Paste or upload a JWT to decode and inspect its header, payload and signature.

Drag & Drop files or code snippets directly into the editor
DECODED TEXT PAYLOAD
Output appears here…

Related Tools

Base64 Encode/Decode

Quickly translate strings or binary data to and from Base64 format.

URL Encode/Decode

Safely encode special characters for query strings and URLs.

HTML Entity Encoder

Safely encode special characters to HTML entities or decode them.

Image → Base64

Convert images to Base64 data URIs for embedding in HTML/CSS.

About this Tool

Safely inspect and parse JSON Web Tokens.

1What is a JSON Web Token (JWT)?

A JWT is a compact, URL-safe means of representing claims to be transferred between two parties. It consists of three distinct parts separated by dots: a Header (defining the hashing algorithm and token type), a Payload (containing the actual claims or user data), and a Signature (used to verify that the sender is who they say they are and to ensure the message wasn't changed along the way).

2Example: Unpacking a JWT Structure

Input JWT: `eyJhbGci...payload...signature` Our tool will instantly extract the payload: ```json { "sub": "1234567890", "name": "John Doe", "admin": true, "iat": 1516239022 } ```

3Deep Dive: Understanding Claims

Common claims like `iss` (Issuer), `exp` (Expiration Time), `iat` (Issued At), and `sub` (Subject) are automatically parsed and translated into human-readable date-time strings. Our decoder also checks for token expiration and provides a real-time warning if the token has expired, helping you debug authentication issues instantly.

4Signature Verification and Security

Unlike basic viewers, this tool allows you to verify the integrity of your JWTs. You can input your HMAC secret or Public Key to check if the signature matches the payload. This is essential for verifying that a token hasn't been tampered with by a malicious party during transit.

5Privacy: Your Auth Tokens Never Leave Your RAM

JWTs are essentially "keys to the kingdom"—they often contain highly sensitive authorization profiles, session data, and user permissions. Secure Devutils unpacks the Base64Url components entirely in your browser's local memory. Your production authentication tokens never leave your device and are never logged or stored on any third-party server.

6Common Use Cases

Security researchers and developers use this decoder to inspect OAuth2 and OpenID Connect (OIDC) tokens, debug "Invalid Token" errors in their applications, and verify that the correct user permissions (scopes) are being included in the session data. It is an indispensable tool for modern web security auditing.

7Decoding JWT in JavaScript (Code Example)

You can decode a JWT payload without a library using standard browser APIs: ```javascript const decodeJwt = (token) => { const base64Url = token.split(".")[1]; const base64 = base64Url.replace(/-/g, "+").replace(/_/g, "/"); const jsonPayload = decodeURIComponent(atob(base64).split("").map(function(c) { return "%" + ("00" + c.charCodeAt(0).toString(16)).slice(-2); }).join("")); return JSON.parse(jsonPayload); }; ```

Privacy Guarantee

Secure Devutils operates exclusively in your browser using local web workers and JavaScript. Your source code, configurations, and sensitive text payloads are never transmitted across the network or stored on any external servers. It is completely safe for air-gapped environments.