codemirror5

CodeMirror 5 is a code editor that runs inside a web browser. Instead of building your own text input area, you can embed CodeMirror into any web application and give users a full-featured editing experience — complete with syntax highlighting (color-coded text that helps visually distinguish different parts of code), support for over 100 programming languages, and add-ons for more advanced editing features.

The problem it solves: plain text boxes (like the default input fields you see in web forms) have no understanding of code. CodeMirror brings a proper code editor experience directly into the browser, so you can add coding tools to any website or web app without requiring the user to install anything.

You would use it if you're building a web application that needs users to write or edit code — for example, an online code playground, a web-based IDE (integrated development environment, meaning a full editor in the browser), a configuration tool, or a template editor. It's customizable through a programming interface and supports CSS-based themes, meaning you can style it to match your app.

Note: this is version 5, which the project describes as legacy. A newer version (CodeMirror 6) exists and is described as more mobile-friendly and more actively maintained. This repository is the source code for version 5, written in JavaScript, and can be installed via npm (a standard JavaScript package manager).