md-viewer

A no-dependency Markdown viewer for macOS Finder. Right-click a .md file → Quick Actions → View Markdown → it opens in your default browser as a split view: the rendered document on the left, the raw Markdown with syntax highlighting on the right.

Built for reading Markdown quickly without opening VS Code — sometimes the formatted view is clearer, sometimes the source is, so you get both at once.

There are two ways to use it:

1. Finder Quick Action (macOS) — right-click a .md file locally.
2. Web app — md.neckarshore.ai — drop, paste, or choose a .md in the browser. Fully client-side; nothing is uploaded.

Features

1. Split view, always — rendered (left) and raw source (right) side by side.
2. Syntax highlighting on the raw side — headings, bullets, bold, links and code fences are colour-coded so structure is visible in the source too.
3. Auto light/dark — follows the macOS appearance setting.
4. Self-contained & offline — the viewer is a single HTML file with all CSS and JS inlined. No internet, no npm, no runtime dependencies.
5. Draggable divider — drag the middle bar to rebalance the two panes.
6. Safe — rendered HTML is sanitized with DOMPurify, so a downloaded .md containing scripts cannot run code.

Install

git clone https://github.com/neckarshore-mmps/md-viewer.git
cd md-viewer
./install.sh

install.sh builds viewer.html, copies the Quick Action into ~/Library/Services/, wires in the absolute path to bin/mdview, validates the plists, and refreshes the Services cache.

Then right-click any .md file in Finder → Quick Actions → View Markdown. If it does not appear, enable it under System Settings → Keyboard → Keyboard Shortcuts → Services → Files and Folders → View Markdown.

Usage

• From Finder: right-click a .md → Quick Actions → View Markdown.
• From the terminal: bin/mdview path/to/file.md

How it works

Piece	Role
bin/mdview	Base64-encodes the file contents + name (so no character can break the HTML), injects them into viewer.html, writes a temp file, and opens it.
viewer.html	Self-contained template built by build.sh. Decodes the payload in-browser, renders the left pane with marked + DOMPurify, highlights the right pane with highlight.js.
quick-action/View Markdown.workflow	Automator Quick Action that runs mdview on the selected file(s). Installed into ~/Library/Services/.

Web app

The same viewer runs as a static, client-side web app in web/index.html (generated by build.sh), served at md.neckarshore.ai. It shares the split view with the Finder tool and adds:

1. Two design themes — Minimalist (black/white/grey, system fonts) and Swiss Grid (IBM Plex, red accent, decorative left index rail, loud theme-scoped header/footer — the default). Pick via the nav dropdown (keyboard typeahead — type a theme's initial letter); the choice persists. Adding a theme is one token block + one dropdown entry.
2. Light/dark toggle — per theme; initial state follows the system, the choice is remembered.
3. README by default — the repo README renders on open; the readme.md button reloads it.
4. Open dialog — the File System Access API (Chrome/Edge) defaults to the Downloads folder and remembers the last-used folder; falls back to a plain file input in Firefox/Safari.
5. Responsive — under 640px the split stacks vertically (rendered on top, source below).
6. Synced scrolling — scrolling either pane drives the other proportionally.
7. Fixed footer + drag-and-drop + paste, all fully client-side.

Fonts are self-hosted (web/fonts/), so the app stays offline-capable. Themes are web-app only — the Finder tool keeps its GitHub styling.

• Deploy: merges to main auto-deploy to production (Vercel project md-viewer, root dir web, git-connected).
• DNS: md.neckarshore.ai is a CNAME → cname.vercel-dns.com at the domain's DNS host (Hostinger), matching the existing www record.

Rebuilding after edits

The committed viewer.html is generated. After editing anything in src/ or updating a vendored library in vendor/, rebuild it:

./build.sh

Updating vendored libraries

Pinned versions live in vendor/ (see docs/vendor-sources.md for the exact URLs and versions). Re-download, then ./build.sh.

Testing

./test/smoke.sh

End-to-end smoke test: builds the viewer, runs mdview on a fixture, and asserts the output is well-formed (placeholders resolved, payload embedded, libraries inlined, missing-file rejected).

Uninstall

./uninstall.sh

Backlog (deliberately not in v1)

1. Synchronized scrolling between the two panes.
2. Configurable / switchable themes beyond auto light/dark.
3. Mermaid diagram and LaTeX math rendering.