md-editor-v3

Md-editor-v3 gives you a split-pane editor with preview, toolbar, and syntax highlighting out of the box. Drop it into your Vue app and you have a working editor in minutes.

MIT license, TypeScript. Features include live preview, table editing, code block syntax highlighting, emoji picker, image upload hooks, Mermaid diagram support, KaTeX math rendering, and customizable toolbars. Also supports React via a companion library (md-editor-rt). Dark mode included.

Fully free. No paid tier, no premium features. Everything (all toolbar options, all rendering modes, all plugins) is included. Solo to large teams: free. It's a component library, not a service. Your only decision is whether it fits your needs.

The catch: this is a Vue-first library. The React port exists but has fewer stars and less community attention. If you're on React, there are more mature options (Tiptap, Milkdown, react-md-editor). Also, the documentation is partially in Chinese; the English docs are functional but not comprehensive. If you hit an edge case, you might be reading source code.