MarkViewer

About

MarkViewer is a free, native Markdown viewer and editor for macOS (10.15+) with a Universal Binary for Intel and Apple Silicon Macs. It opens .md files instantly, renders GitHub-flavored Markdown including tables, checklists, and syntax-highlighted code, and offers live WYSIWYG editing, where formatting is applied as you type Markdown syntax. It works completely offline, with no setup and no internet connection required.

The app is designed to be lightweight and fast. It generates a table of contents from document headings, supports multiple tabs (⌘T) and windows (⌘N), and includes a built-in file finder and terminal. Other features include resizable panels, find-and-highlight search, save status notifications, and Markdown paste that preserves formatting.

MarkViewer also offers optional AI features. You can highlight passages, leave inline review comments, and hand off an editable prompt to Claude, ChatGPT, or another AI tool. It can also run tasks through the Claude Code or Codex CLI already installed on your Mac, without an API key. Agent edits are made to an isolated copy of your folder and shown as a diff, and your file is not changed until you click Apply. The website describes the core app as a fast Markdown viewer and editor, with the AI features as an optional layer.