QL Markdown by XN

QL Markdown is a macOS extension that renders Markdown files in Finder's Quick Look at GitHub-grade quality. Just select a .md file and press the space bar — a clean, well-formatted preview appears instantly with no need to open a separate app.

■ Supported formats

.md, .markdown, .mdown, .mkd extensions

■ Key features

• Full GitHub Flavored Markdown (GFM) support — tables, checkboxes, autolinks, strikethrough

• Automatic YAML Front Matter detection, displayed as a tidy table at the top of the document

• Footnotes and definition lists

• KaTeX math rendering — recognizes $...$, $$...$$, \(...\)

• Mermaid diagrams — flowcharts, sequence, Gantt, class diagrams, etc.

• highlight.js code syntax highlighting (190+ languages)

• Automatic light/dark mode tracking — preview switches instantly when the system appearance changes

■ Fully local operation (network-isolated)

All fonts, scripts, and stylesheets are bundled inside the app. Every feature works identically without an internet connection, and no requests are sent to external servers. http/https requests are double-blocked using both Content Security Policy (CSP) and WKContentRuleList, so you can use the app with confidence in secure environments.

■ App Sandbox compatible

Complies with Apple's App Sandbox and Hardened Runtime. The app does not access any files other than those the user explicitly selects.

■ Local image support (optional)

When a Markdown document references images in the same folder (e.g. ), grant read access to that folder once via the host app's "Grant Folder Access" button, and images will appear in Quick Look as well. When access is not granted, a dotted-box placeholder is shown along with the alt text so you can immediately see which image is missing. http/https images are blocked per the network policy.

■ Large file handling

Markdown files up to 5 MB are processed. Larger files are truncated at a line boundary, and a banner at the top notes the truncation.

Truncated code blocks or math blocks are automatically closed so the output is never broken.

■ Korean / Japanese / Chinese encoding auto-detection

In addition to UTF-8, files saved as UTF-16 (with BOM), Shift-JIS, or EUC-KR are detected automatically and displayed correctly.

■ How to use

1. Launch the app once to register the Quick Look extension.

2. Select a .md file in Finder and press the space bar.

3. (Optional) To view local images, grant folder access from the host app's "Grant Folder Access" button.

■ System requirements

• macOS 14.0 (Sonoma) or later

• Universal binary — Apple Silicon and Intel Macs

■ Open source licenses

The full text of bundled third-party library licenses (cmark-gfm, highlight.js, KaTeX, Mermaid, github-markdown-css) is available in the app menu under Help → "Open Source Licenses".