MacMD Viewer — Markdown with QuickLook and Mermaid Support

https://macmdviewer.com/

Why This Matters

Selecting a .md file in Finder and hitting space gives you, by default, raw text — backslashes, asterisks, code-fence backticks, the whole syntax mess. This was fine when Markdown files came from humans and looked like prose. Now most Markdown that crosses your filesystem is AI-generated: long Claude / ChatGPT outputs saved as .md, design specs with embedded Mermaid diagrams, READMEs from agent runs. Raw-text QuickLook is no longer the right default.
MacMD Viewer is a native macOS app whose entire pitch is "QuickLook for Markdown files, rendered, with Mermaid." Version 1.2.1 just hit Homebrew cask. macOS 14+. $19.99 single license, $39.99 family pack — paid, but one-time.

What It Actually Does

  • QuickLook integration. Spacebar on any .md in Finder renders it as formatted output, no app-open needed. This is the killer feature.
  • Mermaid rendering inline. Flowcharts, sequence diagrams, Gantt charts — rendered, not displayed as a fenced code block of source.
  • Syntax highlighting across 190+ languages for fenced code blocks; theme-aware coloring.
  • Live reload. ~50ms refresh when the file is edited in another app — useful as a side-by-side preview against any editor.
  • Pinch-zoom. Diagrams, tables, code blocks zoom for accessibility / projection.
  • Dark / Light mode. Follows system appearance.

Where It Fits in Our Workflow

The Lossless tree generates Markdown the way other shops generate logs. Every context-v/ file, every changelog/ entry, every Claude Code session transcript is .md. Mermaid is the diagram-of-choice for context-v/specs/ documents. The current ritual for "preview this AI output" is: open VS Code → install a Markdown preview extension → trust its Mermaid renderer (which often lags upstream). MacMD Viewer collapses that to select-file → spacebar.
Two specific intersections:
  1. changelog/ and context-v/ Mermaid blocks. These already exist throughout the tree and currently render only in the splash pages (after maintain splash pages build). MacMD Viewer makes them legible at filesystem-browse time, before any build.
  2. AI-generated .md outputs. Claude Code regularly emits long Markdown reports — research summaries, spec drafts, agent-trace digests. Reading them in raw form is friction; opening every one in a real editor is overkill. Spacebar-to-render is exactly right.
Compare against Marked 2 (the established paid choice, Markdown-focused editor-companion) and Glance (free, QuickLook-only, no Mermaid). MacMD Viewer's specific bet is "Mermaid + QuickLook + AI-friendly defaults" — a niche the existing options leave open.

Install

bash 
brew install --cask macmd-viewer
Free trial in-app, then $19.99 one-time.
Source: https://macmdviewer.com/