https://github.com/breezy89757/READU.md
A fast, lightweight Markdown reader & editor for Windows, built with WinUI 3 and Fluent Design.
https://github.com/breezy89757/READU.md
dark-mode dotnet fluent-design markdown markdown-editor markdown-reader mermaid webview2 windows winui3
Last synced: 2 months ago
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A fast, lightweight Markdown reader & editor for Windows, built with WinUI 3 and Fluent Design.
- Host: GitHub
- URL: https://github.com/breezy89757/READU.md
- Owner: breezy89757
- License: mit
- Created: 2026-02-08T14:40:54.000Z (4 months ago)
- Default Branch: master
- Last Pushed: 2026-02-08T16:29:04.000Z (4 months ago)
- Last Synced: 2026-02-08T21:47:53.515Z (4 months ago)
- Topics: dark-mode, dotnet, fluent-design, markdown, markdown-editor, markdown-reader, mermaid, webview2, windows, winui3
- Language: C#
- Homepage: https://github.com/breezy89757/READU.md
- Size: 518 KB
- Stars: 0
- Watchers: 0
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
Awesome Lists containing this project
- WinUI-3-Apps-List - READU.md - - logo: https://raw.githubusercontent.com/breezy89757/READU.md/refs/heads/master/src/Images/StoreLogo.png --> (📑 Apps List / 🆕 Newly Added Apps!)
README
# READU.md
A fast, lightweight Markdown reader & editor for Windows, built with **Fluent Design**.
[](https://github.com/breezy89757/READU.md/releases/latest)
> **[⬇️ Download Latest Release](https://github.com/breezy89757/READU.md/releases/latest)** — Extract & run, no installation needed.
> **[🛍️ Get it on Microsoft Store](https://apps.microsoft.com/store/detail/9MWGGZBBP1C1?cid=DevShareMCLPCS)**
## Screenshots
| Features & TOC | Mermaid Diagrams |
|:---:|:---:|
|  |  |
| Dark Mode | Edit Mode (Split View) |
|:---:|:---:|
|  |  |
## Features
- **Multi-Tab** — open multiple files simultaneously, with drag-to-reorder tabs
- **Edit Mode** — side-by-side Markdown editor + live preview (`Ctrl+E`)
- **Instant Rendering** — powered by WebView2 (Chromium) and Markdig
- **Syntax Highlighting** — code blocks highlighted via highlight.js
- **Mermaid.js** — flowcharts, sequence diagrams, Gantt charts, and more
- **Smart Mermaid Caching** — SHA256-based incremental DOM updates preserve rendered diagrams
- **Dark Mode** — automatically follows your Windows system theme
- **Table of Contents** — auto-generated sidebar with smooth scroll navigation
- **Drag & Drop** — drop any `.md` file to open it instantly
- **Hot Reload** — automatically refreshes when the file changes externally
- **Scroll & Zoom Persistence** — per-tab scroll position and zoom level preserved across tab switches
- **Print / PDF Export** — `Ctrl+P` to print or save as PDF
- **Full Page Screenshot** — capture the entire rendered page as PNG (`Ctrl+Shift+S`)
- **File Association** — double-click `.md` files to open in READU.md
- **Lightweight** — minimal memory footprint, instant startup with pre-loaded CDN shell
## Keyboard Shortcuts
| Shortcut | Action |
|---|---|
| `Ctrl+O` | Open file (new tab) |
| `Ctrl+W` | Close current tab |
| `Ctrl+Tab` | Next tab |
| `Ctrl+Shift+Tab` | Previous tab |
| `Ctrl+E` | Toggle Edit / Read mode |
| `Ctrl+S` | Save file (edit mode) |
| `Ctrl+N` | New blank tab (edit mode) |
| `Ctrl+P` | Print / Export PDF |
| `Ctrl+Shift+S` | Full page screenshot |
| `Ctrl+` `+` / `-` | Zoom in / out |
| `Ctrl+0` | Reset zoom to 100% |
| `Ctrl+Home` | Open Welcome page |
## Tech Stack
| Component | Technology |
|---|---|
| **Framework** | .NET 9 |
| **UI** | WinUI 3 (Windows App SDK 1.6) |
| **Markdown** | [Markdig](https://github.com/xoofx/markdig) |
| **Rendering** | WebView2 (Chromium) |
| **Syntax Highlighting** | highlight.js (CDN) |
| **Diagrams** | Mermaid.js v11 (CDN) |
| **Window Management** | WinUIEx |
## Architecture & Trade-offs
READU.md is a **WinUI 3 desktop shell** that brings together several open-source libraries. Here's how the pieces fit and what trade-offs were made:
**Markdown parsing** is handled entirely by [Markdig](https://github.com/xoofx/markdig) — a fast, extensible .NET Markdown processor. READU.md doesn't reimplement parsing; Markdig does the heavy lifting and does it well.
**Rendering** uses a WebView2 (Chromium) control. This was a deliberate trade-off: a native text renderer would use less memory, but wouldn't support Mermaid diagrams, LaTeX math, or the full CSS styling that makes Markdown readable. WebView2 is pre-installed on Windows 10/11, so there's no extra download.
**Shell page architecture** — CDN resources (highlight.js, mermaid.js, CSS) are loaded into the WebView2 once at startup. When switching tabs or updating content, only the HTML body is injected via JavaScript (`updateContent()`), avoiding full page reloads. This is what makes tab-switching and edit-mode preview fast.
**Mermaid diagram caching** — each Mermaid code block is hashed (SHA256). During live preview updates, unchanged diagrams keep their rendered SVGs instead of being re-rendered — this prevents the "flash" you'd normally see.
**What this project adds** on top of these libraries:
- Native WinUI 3 app with system theme integration (Mica, dark/light mode)
- Multi-tab document management with per-tab state (scroll, zoom, edit mode)
- File watching with debounced hot-reload
- Full-page screenshot via CDP (`Page.captureScreenshot`)
- File association and drag-and-drop integration
## Build
### Prerequisites
- .NET 9 SDK
- Visual Studio 2022 17.12+ with **Windows application development** workload
- Windows 10 (1903+) or Windows 11
### Build & Run
```bash
# Clone
git clone https://github.com/breezy89757/READU.md.git
cd READU.md
# Build
dotnet build src\READU.md.csproj -p:Platform=x64
# Or open READU.md.sln in Visual Studio and press F5
```
## Settings
Settings are stored at `%LOCALAPPDATA%\READU.md\settings.json`:
```json
{
"properties": {
"enable_mermaid": { "value": true },
"font_size": { "value": 14 }
}
}
```
## Contributing
Contributions are welcome! Please open an issue to discuss your idea before submitting a PR.
## License
[MIT](LICENSE)