Web Markdown Editor

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A lightweight, single-file Markdown editor with live preview, syntax highlighting, math formulas, and diagram rendering. It runs directly in a modern browser—no installation, dependencies, or server required.

Try the online editor

✨ Features

• ✅ English and Simplified Chinese interface with automatic browser-language detection
• ✅ Live Markdown preview
• ✅ Syntax highlighting for multiple programming languages
• ✅ KaTeX math rendering
• ✅ Mermaid diagrams with a dedicated viewer, zoom, pan, and PNG/SVG downloads
• ✅ PDF, PNG, and HTML export
• ✅ Multiple themes and independent light/dark mode
• ✅ Table of contents and synchronized scrolling
• ✅ Local file open/save through the File System Access API
• ✅ Drag-and-drop Markdown files
• ✅ Fully offline edition

📸 Screenshot

🚀 Quick start

Online edition

Open markdown-editor.html in a browser or use the hosted demo above.

📥 Download markdown-editor.html

Offline edition

Use this edition on an intranet or without an internet connection.

1. 📥 Download web-markdown-editor-offline.zip
2. Extract the archive anywhere.
3. Open markdown-editor-offline.html in a browser.
4. Start editing—no network connection is required.

See the offline edition guide for details.

Desktop edition

The Electron desktop application now lives in web-markdown-editor-desktop. This repository remains focused on the lightweight web and offline HTML editions.

📦 Editions

Edition	File	Description
Online	markdown-editor.html	Uses CDN resources and requires a network connection
Offline	offline/markdown-editor-offline.html	Uses local assets and runs without a network connection

🔨 Build the offline edition

Only the online source file needs to be maintained. Generate the offline edition with:

node build-offline.js

The build script:

1. Reads markdown-editor.html.
2. Replaces CDN URLs with local assets/ paths.
3. Writes offline/markdown-editor-offline.html.

When adding a CDN dependency, add its mapping to build-offline.js:

1. Add <link> and <script> replacements to replacementRules.
2. Add JavaScript URL replacements to themeUrlMappings.

🛠️ Technology

• Frontend: Vanilla HTML, CSS, and JavaScript
• Markdown: Marked.js
• Syntax highlighting: Highlight.js
• Math: KaTeX
• Diagrams: Mermaid.js
• UI: Bootstrap 5
• Export: html2pdf.js and html2canvas

📄 License

MIT License