mdLens

Lightweight macOS-native markdown viewer. No Electron, no bloat.

2.3 MB binary / ~15 MB memory / instant startup

Built with SwiftUI + WKWebView and a single dependency (swift-markdown).

Features

• Syntax Highlighting — 190+ languages via highlight.js, theme-aware
• Math / LaTeX — Inline $...$ and display $$...$$ via KaTeX
• Mermaid Diagrams — Flowcharts, sequence diagrams, and more
• GitHub Admonitions — NOTE, TIP, IMPORTANT, WARNING, CAUTION
• Footnotes — Reference-style footnotes with back-links
• Emoji Shortcodes — ~200 common shortcodes (:rocket: → 🚀)
• Sidebar — File tree, heading outline, article list
• Themes — Auto / Light / Dark / Sepia
• File Watching — Auto-reload on external changes (FSEvents)
• Quick Open — Cmd+P fuzzy file search
• Drag & Drop — Drop .md files or folders to open

Install

Download mdLens.app from Releases and move to /Applications.

Signed and notarized with Developer ID.

Build from Source

Requires macOS 14+ and Swift toolchain (Xcode Command Line Tools is enough).

# Run directly
swift run mdLens

# Release build
swift build -c release

# Create .app bundle (requires Developer ID certificate)
bash scripts/build-app.sh

Keyboard Shortcuts

Shortcut	Action
Cmd+O	Open file
Cmd+Shift+O	Open folder
Cmd+P	Quick Open
Cmd+Shift+L	Toggle sidebar
Cmd+W	Close window

Architecture

Sources/MarkdownViewer/
├── App/           # Entry point, state, menu commands
├── Models/        # Document, file tree, outline
├── Services/      # Renderer, file watcher, parser, emoji map
├── Views/         # Content, sidebar, document, settings
├── Theme/         # Light/Dark/Sepia theme definitions
└── Extensions/    # String utilities

Markdown → swift-markdown AST → HTML (custom visitor) → WKWebView.

Heavy JS libraries (KaTeX, Mermaid) are lazy-loaded from CDN only when the document needs them.

License

MIT