Warning

JUSTC language is currently in development and is experimental!

Documentation is coming after release of new Just an Ultimate Site Tool update. Currently, you can use experimental JUSTC demo website.

JUSTC

JUSTC is a powerful scripting language designed for automation, with JavaScript™ and Luau included, designed to be backwards compatible with JSON.

JUSTB is a bytecode format and a part of JUSTC, designed for faster loading and smaller file sizes.
JUSTO is an object notation language with simple syntax, designed for easy and fast parsing, also a part of JUSTC.

JUSTC is a free and open-source software, made for Just an Ultimate Site Tool, the Web, and everything else.

Features

• JUSTC is compilable to .justb (JUSTB);
• Interpretable;
• Serializable to JSON, JUSTO, XML, YAML;
• Cross-platform: Windows, Linux, macOS, WebAssembly (JavaScript - Node.js and browsers).

Quick Start

CLI

justc --help

Web

<script src="https://unpkg.com/justc"></script>
<script>
    await JUSTC.initialize();
    await JUSTC.execute(`
        echo "Hello, World!".
    `);
</script>

Node.js

npm install justc

const JUSTC = require("justc");

JUSTC.execute(`
    echo "Hello, World!".
`).then(result => console.log(result));

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License

JUSTC, JUSTB, and JUSTO are open-source software, licensed under the MIT License.

Copyright (c) 2025-2026 JustStudio. (The dot in "JustStudio." is part of the name.)

For Web Developers

If you are using the official JUSTC distribution from just.js.org/justc, unpkg.com/justc or npm, attribution is not required in your website's UI or source code.

We have already included:

• License headers in all scripts
• Source maps with license headers
• LICENSE and README.md files in the distribution
• Copyright notices in WASM binary custom sections

Otherwise, or if your website blocks source map loading in some way, please include the Desktop/Mobile Applications notice.

For Desktop/Mobile Applications

If your application uses JUSTC, or at least JUSTB or JUSTO, please include the following notice in your credits or about screen:

This software uses JUSTC, JUSTB and JUSTO,
licensed under the MIT License.
Copyright (c) 2025-2026 JustStudio.
(The dot in "JustStudio." is part of the name.)
https://just.js.org/justc
https://juststudio.is-a.dev

For Developers Building from Source

If you compile JUSTC from source or distribute it as part of your project, you must include the MIT License notice. See LICENSE for details.

Logo and banner

Attribution making use of the JUSTC logo or JUSTC banner is also encouraged when reasonable.

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Dependencies

JUSTC uses C++ as its implementation language. The entire project requires C++17.

JUSTC incorporates code from the following open-source projects:

Core Dependencies (Native Builds - Linux/macOS/Windows)

• Cereal by iLab @ USC — Licensed under the BSD-3-Clause license:
  Copyright (c) 2013-2022, Randolph Voorhies, Shane Grant.
  https://github.com/USCiLab/cereal/blob/master/LICENSE

• CPR by libcpr — Licensed under the MIT License:
  Copyright (c) 2017-2021 Huu Nguyen.
  Copyright (c) 2022 libcpr and many other contributors.
  https://github.com/libcpr/cpr/blob/master/LICENSE

• ICU by Unicode — Licensed under the UNICODE LICENSE V3:
  Copyright (c) 2016-2025 Unicode, Inc.
  https://github.com/unicode-org/icu/blob/main/LICENSE

• Luau by Roblox — Licensed under the MIT License:
  Copyright (c) 2019-2025 Roblox Corporation.
  Copyright (c) 1994–2019 Lua.org, PUC-Rio.
  https://github.com/luau-lang/luau/blob/master/LICENSE.txt

• nlohmann/json by Niels Lohmann — Licensed under the MIT License:
  Copyright (c) 2013-2026 Niels Lohmann.
  https://github.com/nlohmann/json/blob/develop/LICENSE.MIT

• QuickJS by bellard — Licensed under the MIT License:
  Copyright (c) 2017-2021 Fabrice Bellard.
  Copyright (c) 2017-2021 Charlie Gordon.
  https://github.com/bellard/quickjs/blob/master/LICENSE

• QuickJS CMake by Rob Loach — Licensed under the MIT License:
  Copyright (c) 2022 Rob Loach.
  https://github.com/RobLoach/quickjs-cmake/blob/master/LICENSE

WebAssembly

• Does not use CPR (HTTP Requests support via XHR API)
• Does not use nlohmann/json
• Does not use QuickJS and QuickJS CMake
• Does not use ICU (Unicode support via Intl API)

Reference / Inspiration

• Lua by PUC-Rio — Licensed under the MIT License: Copyright (c) 1994-2025 Lua.org, PUC-Rio. https://www.lua.org/license.html (Luau is a fork of Lua)

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Acknowledgements

• JavaScript™ is a trademark of Oracle Corporation. For more information, see https://www.oracle.com/legal/trademarks/

• Special thanks to the authors and maintainers of: Cereal, CPR, ICU, Lua, Luau, nlohmann/json, QuickJS and QuickJS CMake for their excellent work, which made JUSTC possible.