MDViewer

A lightweight, native macOS Markdown viewer built for developers.

Overview

MDViewer was created out of a simple need: a fast, minimal way to read .md files when working from the terminal with tools like Claude Code or Codex. It renders Markdown beautifully without the overhead of a browser or a full editor.

MDViewer started as a viewer — but we wanted editing too, so it now includes a built-in split-view editor.

Features

• Instant rendering — opens and renders Markdown files immediately
• Live reload — watches for file changes and re-renders as you save
• Table of contents — auto-generated sidebar from headings with smooth scroll
• Syntax highlighting — 27 languages via Shiki v1
• Math equations — inline and block LaTeX via KaTeX
• Mermaid diagrams — flowcharts, sequence diagrams, Gantt charts, and more
• Smart link handling — local .md links open in-app; external links open in the browser
• Export to PDF — one-click PDF export preserving all styles
• Signed & notarized — Developer ID signing and Apple notarization

Editor Mode

Toggle the built-in editor with ⌘E or the pencil button in the toolbar.

• Split view: Editor on the left, live preview on the right
• New file: ⌘N, the toolbar button, or the welcome screen starts a blank document in editor mode
• Save: ⌘S saves changes to the current file; for a new (untitled) document it shows a save panel
• Unsaved changes are indicated by the Save button becoming active
• Closing the window, or starting a new file, with unsaved changes prompts Save / Discard / Cancel

Help

Open "MDViewer Help" from the Help menu for a live-rendered reference covering all Markdown syntax and every Mermaid diagram type (flowchart, sequence, class, state, ER, Gantt, pie, user journey, mindmap, timeline).

Requirements

• macOS 14 Sonoma or later
• Apple Silicon (M1 or later)

Installation

1. Download the latest MDViewer-x.x.x.zip from the Releases page
2. Unzip and drag MDViewer.app to your Applications folder
3. Double-click any .md file — or drop it onto the MDViewer icon in the Dock

Building from source

Requires Xcode 15 or later.

git clone https://github.com/Masakai/mdviewer.git
cd mdviewer
open MDViewer.xcodeproj

Build and run with ⌘R. No Swift Package dependencies — all vendor libraries are bundled in MDViewer/Resources/Web/vendor/.

Tech stack

Layer	Technology
UI framework	SwiftUI + AppKit
Rendering engine	WKWebView
Markdown parser	marked v12
Syntax highlighting	Shiki v1
Math	KaTeX v0.16
Diagrams	Mermaid v10
File watching	DispatchSource (kqueue)

Open source libraries

All bundled libraries are MIT licensed. See THIRD_PARTY_NOTICES.md for full license texts.

Library	Version	License
marked	12.0.2	MIT
Shiki	1.x	MIT
KaTeX	0.16.11	MIT
Mermaid	10.x	MIT

License

MDViewer is released under the MIT License.

© 2026 Masanori Sakai