CodeMirror

CodeMirror 6 is built from small modules: language support, themes, linting, autocompletion and key bindings are all extensions you add. Highlighting uses Lezer, an incremental parser that re-reads only what changed, so large files stay responsive, and the editor was designed with touch screens and screen readers in mind. Its author, Marijn Haverbeke, also created ProseMirror, the engine under TipTap.

The main alternative is Monaco, the editor from VS Code, which brings more IDE features out of the box but is heavier and does not support mobile browsers. CodeMirror suits code playgrounds, SQL consoles, config editors, Markdown source editing and in-app scripting. It edits plain text; for formatted documents with bold and images, a rich text toolkit such as TipTap fits instead.