What is lengyi-markdown-editor?

This project is a Markdown editor that lives entirely in a single HTML file. There is nothing to install and no account to create. You just download the file, double-click it, and start writing in your browser, with everything staying on your own computer. The editor shows your raw Markdown on one side and a live rendered preview on the other, and you can switch between edit-only, preview-only, or split views, dragging the divider wherever you like. It includes the usual formatting tools you would expect: headings, bold and italic text, lists, blockquotes, code blocks, tables through a visual picker, and find and replace. It also supports math formulas through KaTeX and diagrams through Mermaid, so mind maps and flowcharts can be written directly in Markdown and rendered in the preview. Content is automatically saved to the browser's local storage every half second, along with your filename, layout, and preferred theme and language, so a page refresh will not lose your work. The interface is available in ten languages, including English, Simplified and Traditional Chinese, Japanese, Korean, and several European languages. You can export your document as plain Markdown, a standalone HTML file, a Word document, a PDF through the browser's print function, or a long image sized for social media sharing. Under the hood it is built with plain HTML, CSS, and JavaScript, with no framework, relying on the marked.js library to render Markdown. An optional local Python proxy script is included for converting a webpage into Markdown, which needs to be run separately if you want that feature. The author built the tool for their own writing needs and mentions it works well alongside AI coding agents for editing files like AGENTS.md or Skill.md. The project is released under the MIT license, though the README adds that commercial use should have separate authorization from the author.