Simple Markdown Viewer

A lightweight, fast markdown and Mermaid viewer and editor for Windows, macOS and Linux, built with Avalonia UI.

Website: https://smv.dabworx.com/

Download

Get the latest version from Releases or the website. The app lets you know when a newer version is available (see Update Checks).

Platform	Download	Notes
Windows 10 and 11	SimpleMarkdownViewer-Setup-X.Y.Z.exe	Installer; can set up file associations
macOS 14 or later, Apple Silicon	SimpleMarkdownViewer-X.Y.Z-macos-arm64.dmg	Drag the app to Applications
macOS 14 or later, Intel	SimpleMarkdownViewer-X.Y.Z-macos-x64.dmg	Drag the app to Applications
Ubuntu and Debian	simplemarkdownviewer_X.Y.Z_amd64.deb	Installs WebKitGTK for you
Other Linux	SimpleMarkdownViewer-X.Y.Z-linux-x86_64.AppImage	Needs WebKitGTK 4.1 (see Platform Notes)

macOS and Linux downloads are available from version 1.5.2 on. They're newer than the Windows version, so please open an issue if something doesn't work.

First launch on macOS: the app isn't notarized by Apple yet, so macOS blocks it the first time you open it. Open it once, then go to System Settings > Privacy & Security and choose Open Anyway. You only need to do this once.

Installing on Linux:

# Ubuntu and Debian
sudo apt install ./simplemarkdownviewer_X.Y.Z_amd64.deb
simplemarkdownviewer notes.md

# Any distro, with WebKitGTK 4.1 installed
chmod +x SimpleMarkdownViewer-X.Y.Z-linux-x86_64.AppImage
./SimpleMarkdownViewer-X.Y.Z-linux-x86_64.AppImage notes.md

Features

• Live Reload - The preview updates in place when the file changes on disk, keeping your scroll position
• Tabs - Open multiple markdown and Mermaid files at once
• Edit Mode - Split view with a syntax-highlighted editor and live preview (Ctrl+E), plus a Format menu on right-click (bold, italic, links, headings, lists, code blocks, and more)
• New, Save, Save As - Create documents from scratch and save them; you're prompted before closing unsaved changes
• Dark/Light Mode - Toggle with persisted preference
• Custom CSS - Restyle the preview for each theme (see Custom CSS)
• Syntax Highlighting - Code blocks with highlight.js
• Mermaid Diagrams - Flowcharts, sequence diagrams, and standalone .mmd / .mermaid files; click a diagram to view it full screen with zoom and pan
• KaTeX Math - Inline $...$ and display $$...$$ LaTeX math
• Preview Line Numbers - Show source line numbers beside the preview (View menu)
• Links - Web links open in your browser, links to other markdown files open in a new tab, and relative images load from the document's folder
• Drag & Drop - Drop markdown or Mermaid files onto the window
• Clipboard Paste - Open clipboard text as a new untitled document (Ctrl+Shift+V)
• Recent Files - Quick access to recently opened files
• Print/PDF - Print or save as PDF via the system print dialog
• File Association - The Windows installer can register the app for markdown and Mermaid files, and the Linux .deb adds it to Open With (see File Associations)
• Safe Preview - Scripts embedded in a markdown file never run, so opening files from anywhere is safe; ordinary HTML such as <details> or <img> still renders

Supported file types: .md, .markdown, .mdown, .mkd, .mkdn, .mdwn, .mdtxt, .mdtext, .mdx, .rmd, .mmd, .mermaid

Keyboard Shortcuts

Shortcuts use Ctrl on every platform, including macOS (not Cmd).

Shortcut	Action
Ctrl+N	New document
Ctrl+O	Open file
Ctrl+S	Save (in edit mode)
Ctrl+Shift+S	Save as (in edit mode)
Ctrl+E	Toggle edit mode
Ctrl+B / Ctrl+I / Ctrl+K	Bold / italic / link (in edit mode)
Ctrl+W	Close tab
Ctrl+Shift+V	New from clipboard
Ctrl+Shift+C	Copy markdown to clipboard
Ctrl+P	Print
F5	Refresh (also reapplies custom CSS)
F12	Dev tools
Esc	Close full-screen diagram

Custom CSS

Choose View > Open Custom CSS to create and open custom-dark.css or custom-light.css (for the current theme), pre-filled with the built-in styles. Edit and save it, then press F5 to apply. Delete the file to go back to the defaults.

These files live in the settings folder along with settings.json:

• Windows: %LocalAppData%\SimpleMarkdownViewer
• macOS: ~/Library/Application Support/SimpleMarkdownViewer
• Linux: ~/.local/share/SimpleMarkdownViewer

Update Checks

At most once a day, when the app starts, it asks GitHub for the latest release version. If there's a newer one, a notice appears at the top of the window with a Download button (which opens the release page) and a Dismiss button. Nothing is downloaded or installed automatically, and no information about you or your files is sent.

You can check manually with Help > Check for Updates, or turn automatic checks off with Help > Check for Updates Automatically.

Platform Notes

• Windows: Uses WebView2, which is pre-installed on Windows 10 and 11.
• macOS: Needs macOS 14 or later and uses the built-in WKWebView. Double-clicking a markdown file in Finder doesn't open it in the app yet; use File > Open or drag the file onto the window.
• Linux: Needs WebKitGTK 4.1. The .deb installs it for you; for the AppImage or a source build, install it with:
  • Ubuntu/Debian: sudo apt install libwebkit2gtk-4.1-0
  • Fedora: sudo dnf install webkit2gtk4.1
  • Arch: sudo pacman -S webkit2gtk-4.1

Settings are stored per user, in the folder listed under Custom CSS.

Building from Source

Prerequisites

• .NET 10.0 SDK

Clone and Build

git clone https://github.com/KrunchMuffin/SimpleMarkdownViewer.git
cd SimpleMarkdownViewer
dotnet build
dotnet run

Publish

Windows

dotnet publish -c Release -r win-x64 --self-contained -o publish

macOS (Intel)

dotnet publish -c Release -r osx-x64 --self-contained -o publish

macOS (Apple Silicon)

dotnet publish -c Release -r osx-arm64 --self-contained -o publish

Linux

dotnet publish -c Release -r linux-x64 --self-contained -o publish

Installers and Packages

Release downloads for every platform are built by GitHub Actions (release.yml): pushing a version tag builds the Windows installer, the macOS disk images and the Linux .deb and AppImage, checks that the macOS and Linux builds start and render a document, and attaches everything to a draft release. See CONTRIBUTING.md for the steps.

To build the Windows installer on your own machine:

1. Install Inno Setup 6
2. Run build-installer.bat from a Command Prompt
3. The installer will be in the installer folder

The macOS and Linux packaging files are in packaging/.

File Associations

Windows

The installer offers checkboxes to make Simple Markdown Viewer the default app for:

• Common extensions: .md, .markdown
• Extended extensions: .mdown, .mkd, .mkdn, .mdwn, .mdtxt, .mdtext
• Specialized extensions: .mdx, .rmd
• Mermaid extensions: .mmd, .mermaid

For each group you tick, the app becomes the default and is added to Open with for those file types. To change the default later, right-click a file → Open with → Choose another app. Uninstalling removes the associations.

Linux

The .deb adds Simple Markdown Viewer to Open With for markdown files. To make it the default, right-click a .md file in your file manager and choose it under Open With (the wording varies by desktop).

macOS

Not supported yet: the app can't be set as the default for markdown files in Finder. Open files with File > Open or by dragging them onto the window.

Tech Stack

• Avalonia UI - Cross-platform .NET UI framework
• Avalonia WebView - Native web view (WebView2 / WKWebView / WebKitGTK)
• AvaloniaEdit - Text editor with TextMate syntax highlighting
• Markdig - Markdown parser
• highlight.js - Syntax highlighting
• Mermaid - Diagrams
• KaTeX - Math rendering

Contributing

Bug reports, ideas, and pull requests are welcome. See CONTRIBUTING.md to get started, and please follow the Code of Conduct.

Security

Please report security problems privately, as described in SECURITY.md.

License

MIT License, © 2026 DAB Worx Inc. See the LICENSE file.