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FluxMarkdown registers itself with macOS as a QuickLook provider for a wide range of Markdown-adjacent file types. When you press Space on any of the files listed below in Finder, FluxMarkdown handles the preview — rendering it as formatted Markdown rather than showing plain text.
macOS uses the Uniform Type Identifier (UTI) system to match files to QuickLook providers. FluxMarkdown declares a set of exported UTIs in its Info.plist (via UTExportedTypeDeclarations) so that macOS recognizes each extension and routes it to the FluxMarkdown extension. On macOS Ventura and later, FluxMarkdown also uses pluginkit -e use at install time to explicitly activate the extension and set its priority, ensuring it is not pre-empted by older or conflicting plugins.

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Supported extensions

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Standard Markdown

ExtensionFormatNotes
.mdStandard MarkdownThe most common Markdown extension; recognized universally.
.markdownStandard MarkdownLong-form alternative to .md; fully equivalent.

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Extended and specialized formats

ExtensionFormatNotes
.mdxMDX (Markdown + JSX)Used in React and Next.js documentation. JSX syntax is not executed; content is rendered as Markdown.
.rmdR MarkdownUsed with RStudio for reproducible research documents. Code chunks are rendered as code blocks.
.qmdQuarto MarkdownUsed with the Quarto publishing system. Rendered as Markdown; execution directives appear as code blocks.
.mdocMarkdocStructured Markdown dialect used by Stripe and others.
.livemdLivebookElixir ecosystem notebook format used with Livebook.

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Mermaid diagram files

ExtensionFormatNotes
.mmdMermaid diagramSpecial handling: see below.

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Markdown variant extensions

ExtensionFormatNotes
.mkdMarkdown variantAlternative extension in common use.
.mkdnMarkdown variantAlternative extension in common use.
.mkdownMarkdown variantAlternative extension in common use.
.mdwnMarkdown variantAlternative extension used by ikiwiki and similar tools.
.mdownMarkdown variantAlternative extension in common use.

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Special handling for .mmd files

.mmd files are pure Mermaid diagram source files — they contain only diagram syntax without any surrounding Markdown. When FluxMarkdown opens a .mmd file, it automatically wraps the entire file content in a Mermaid fenced code block before rendering: 
```mermaid
<your .mmd file content here>


This means every Mermaid diagram type is supported in `.mmd` files — flowcharts, sequence diagrams, Gantt charts, class diagrams, entity-relationship diagrams, and more — without any modification to the file.

<Note>
  The Mermaid toggle in **Settings → Rendering** does not affect `.mmd` files. Those files are always rendered as diagrams.
</Note>

## How FluxMarkdown registers as the QuickLook handler

When you install and launch FluxMarkdown, macOS registers the app's QuickLook extension via `pluginkit`. The extension declares each supported file extension and its corresponding UTI in the app bundle. macOS then uses these declarations to route Space-bar previews for matching files to FluxMarkdown.

On macOS Ventura and later, FluxMarkdown explicitly activates the extension using `pluginkit -e use` to avoid being displaced by cached or previously installed plugins.

## If a file type is not recognized

If pressing **Space** on a supported extension shows plain text or uses a different previewer, the QuickLook cache may be stale or another plugin may have higher priority.

**Step 1 — Reset the QuickLook cache:**

```bash
qlmanage -r
killall Finder
Step 2 — Check which plugin handles your file type: 
qlmanage -m
This prints a list of all registered QuickLook generators and the UTIs they handle. Look for your file extension and confirm that the entry points to FluxMarkdown. Step 3 — Check that the extension is active: 
pluginkit -m -v | grep -i markdown
If FluxMarkdown does not appear or is marked as disabled, try relaunching the FluxMarkdown app — it re-registers the extension on each launch. Step 4 — Verify the app location: macOS sandbox restrictions require FluxMarkdown to live in /Applications/. If the app is in ~/Downloads/, ~/Desktop/, or any other location, the QuickLook extension may not activate. Move the app to /Applications/ and relaunch.

Diagrams and charts

Mermaid, Vega, and Graphviz rendering details

Troubleshooting

Fix QuickLook registration and preview issues

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