Inspiration
macOS has a reader for almost every file you own. Open a PDF and Preview handles it. Open a .md file and you get TextEdit showing raw text — even though AI agents like Claude and Cursor now generate Markdown by default, and those files pile up faster than anything else on disk.
That gap is the whole project: the reader Apple never shipped.
What it does
MacMD Viewer renders Markdown on macOS, read-only by design.
- Press Space on any
.mdfile in Finder and it renders in Quick Look - Double-click to open it properly — live reload when the file changes on disk
- Mermaid diagrams, syntax highlighting, document outline, native tabs
- 12 document themes, light and dark
- Works entirely offline
Read-only is a decision, not a limitation. You keep the editor you already like; this handles the read side.
How we built it
Native SwiftUI with a WKWebView rendering layer, plus a Quick Look preview extension so Finder renders .md without launching the app. Universal binary, notarized. The renderer and the Quick Look extension share the same pipeline so a file looks identical in both.
Challenges we ran into
Quick Look extensions run in a sandboxed process with a tight memory budget and no persistent state, so the rendering pipeline had to be rebuilt to work identically inside it. Native window tabbing under SwiftUI also required dropping to AppKit — automatic tabbing never engages on its own there.
What's next
Better handling of large documents and local image resolution inside sandboxed previews.
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