JWT Token Builder & Signer
Generate and sign standards-compliant JSON Web Tokens (JWT) using HMAC algorithms with real-time signature verification and one-click presets.
At a glance
JWT Token Builder & Signer is a free web tool that builds, customizes claims, signs, and verifies JSON Web Tokens (JWT) using HMAC algorithms (HS256, HS384, HS512) directly in your browser. Support for HS256 (HMAC-SHA256), HS384 (HMAC-SHA384), and HS512 (HMAC-SHA512) using native Web Crypto APIs. Your inputs never leave your device, and there is no sign-up or install.
100% In-Browser JWT Token Builder & Signer
Build, sign, and verify JSON Web Tokens client-side using Web Crypto HMAC (HS256, HS384, HS512). Your secret keys never leave browser memory.
HMAC Signature Integrity
HMAC (Hash-based Message Authentication Code) uses a shared secret to generate a cryptographic checksum of the header and payload. Any modification to claims immediately invalidates the signature.
Always Set Expiration ('exp')
Stateless tokens cannot be revoked without a blacklist. Always assign a short-lived expiration (exp) such as 15 minutes to 24 hours to limit the blast radius of stolen tokens.
Key Entropy Requirements
For HS256, use secrets with at least 256 bits (32 bytes) of cryptographic randomness. Weak dictionary passwords allow offline brute-force attacks via tools like Hashcat.
Why Use This JWT Token Builder & Signer?
How to Use JWT Token Builder & Signer
Configure Header & Claims
Select your signing algorithm (HS256, HS384, HS512) and edit your payload JSON claims, or load a preset.
Enter or Generate Secret Key
Type your HMAC secret key or click "Generate Random" to create a cryptographically secure 256-bit key.
Copy Signed Token
Copy the compact JWT token or the formatted "Bearer <token>" authorization header for your API requests.
Worked example: JWT Token Builder & Signer
Executed entirely inside your local browser memory using modern Web APIs. The engine verifies input syntax, performs deterministic transformation, and exposes instant copy or download options.
sample_payload.json (Valid format conforming to JSON specification)
converted_result.jwt (100% client-side)
Technical Specifications & Engine Details
| Specification | Details |
|---|---|
| Supported Formats | JSON, TEXT → JWT, TEXT |
| Execution Mode | 100% Client-Side In-Browser (client) |
| Browser Requirements | Requires modern web browser with Web Cryptography API (SubtleCrypto). |
| Performance Constraints | Client browser memory limit (typically 1–2 GB RAM); processing speed depends on local device CPU. |
100% Client-Side Privacy Guarantee
All cryptographic HMAC operations execute 100% locally in your web browser. No secret keys or payload claims ever leave your device.
Frequently Asked Questions
What algorithms does this JWT builder support?
Are my secret keys sent to any server?
What is the difference between HS256 and RS256?
Can I verify an existing token with my secret?
Methodology
This tool runs entirely in your browser. The example above shows a representative input and the result it produces.
Last updated .