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Prerequisites

Software and Hardware Requirements​

A Computer​

You will need a computer (Windows, macOS and Linux all work) to mod Scratch 3.0. You will also need to be able to install software on it. If you do not have a computer or are unable to install software on the computer, you might be able to use an online service like GitHub Codespaces, Replit or Glitch.

A Web Browser​

As Scratch 3.0 runs in a web browser, you will need a web browser. Since you are reading this, you probably already have one. Any browser that works with Scratch 3.0 will be fine.

A Code Editor​

You will need a code editor to write code for your Scratch mod in. You could technically use any text editor, but you should use an editor designed for code, as they generally provide useful features like syntax highlighting, suggestions and other useful code-specific features.

Here are some code editors:

Node.js​

Node.js is used by Scratch's development tools. You can download Node.js here.

A Node.js Package Manager (NPM, Yarn, PNPM, etc.)​

You need a Node.js package manager to install Scratch's depenedncies. Node.js comes with NPM, but you could also use Yarn or PNPM.

Git is a version control system. Using Git well will allow you to view older versions of your mod and, with GitHub, allow you to collaborate with others to make a mod. Using Git also allows you to more easily release your mod using GitHub and GitHub Pages.

Windows Subsystem for Linux (WSL) Only needed for Windows​

scratch-blocks doesn't work well on Windows, so I recommend using Windows Subsystem for Linux for scratch-blocks. You can continue to use regular Windows for the rest of your mod. You can find out how to install WSL here.

Python scratch-blocks​

note

Older versions of scratch-blocks depend on an old unsupported version of Python. The version of Python required is Python 2, the latest version of Python 2 is 2.7.18 from April 2020 and can be found here.

In case you are modding with an older version of scratch-blocks, you can install Python 2 with these commands:

sudo apt update
sudo apt install python2

scratch-blocks's build script depends on Python. You can download Python from their website here.

If using Ubuntu Linux (the default distro for WSL), you can use these commands to install Python:

sudo apt update
sudo apt install python3 python-is-python3

Java scratch-blocks​

scratch-blocks uses Google's Closure Compiler, which uses Java, so you will need to have Java installed.

Useful Knowledge​

JavaScript is the main language used by Scratch 3.0. Knowing at least the basics of JavaScript will be very helpful in modding Scratch 3.0.

You need to use some commands to setup, build and run Scratch 3.0. You should at least know how to launch the command line on your computer or in your code editor and how to navigate your computer with it (cd, dir/ls, etc.).

  • Windows: Windows Terminal, Command Prompt or Windows PowerShell
  • macOS: Terminal
  • Linux: The exact name may depend on Linux distribution. Ubuntu calls it Terminal.

If you want to use Git and GitHub, you will need to know at least how to clone a repository and commit. If you want to use GitHub, you will also need to know how to fork a repository on GitHub and push to the repository.

CommonJS (specifically, require and module.exports)​

Scratch 3.0 is made up of many files and packages and needs a way to use resources from another file (require) and a way to make resources available from a file (module.exports).

HTML​

While HTML is not really used much by Scratch, the concepts can be useful for JSX, which is needed to modify Scratch's interface.

CSS​

Knowledge of CSS is useful for modifying the appearance of the Scratch interface.

React and JSX​

scratch-gui (the user interface for Scratch 3.0) uses React for the user interface. If you want to modify the interface, it will be useful to know it. Scratch also uses JSX, which is just JavaScript with the ability to write a strict form of HTML directly in the JavaScript.