Press space in Finder

Press space. There is your document.

Twain installs a real Finder Quick Look preview for .md and .mdx, so Markdown behaves like a first-class file on your Mac rather than mystery text.

The short version

Markdown files on a Mac usually preview as plain text, if at all. With Twain installed, selecting a file and tapping space shows it fully rendered: headings, tables, maths, Mermaid diagrams and highlighted code, right in Finder, with no app window opened. The same preview covers .mdx, which almost nothing else on macOS previews at all.

What the space bar gets you

The app's exact renderer, running inside Finder.

quick look · .md

Preview Markdown in Finder Free

Select any .md file and tap space. It renders in place, fully styled, without opening an app.

quick look · .mdx

Preview MDX in Finder Free

The same instant preview for .mdx, safely rendered: known components as real UI, unknown ones as labelled placeholders.

same engine

The app's exact rendering Free

Quick Look uses the identical renderer as the app and the CLI, so the preview is the document, not an approximation.

always blocked

No tracking pixels Free

In Quick Look a WebKit rule blocks every remote subresource, always, so previewing someone else's document can never load a tracking pixel.

assets

Relative images, honestly stated Free

In the app, local relative images resolve against the document's folder, including nested paths and names with spaces. Finder previews can't read them yet, a macOS sandbox limit.

stays current

Live refresh in the app Free

When an agent or another program rewrites the open file, the app's view updates on its own. Essential when documents are generated while you watch.

A Finder window with an .mdx file selected, and the Quick Look preview beside it rendering the document with its heading, prose and colour-coded callouts. — The same renderer drives the Finder Quick Look preview. Remote subresources are always blocked there.

How macOS chooses a Quick Look preview

macOS shows the spacebar preview belonging to your default Markdown app. Twain offers a one-click button to make itself the default; after that, space on any .md or .mdx shows Twain's preview. If another Markdown app holds the default, its preview wins, whatever it looks like.

Safe on files you did not write

A Quick Look preview renders unprompted the moment you press space, so it has to assume the file is hostile. Twain's preview never executes anything in a document, always blocks remote subresources at the WebKit level, and writes nothing: previewing a file leaves no trace in it.

Questions

Why does pressing space not show Twain's preview?

macOS uses the Quick Look preview of your default Markdown app. Open Twain and use its one-click button to become the default; from then on the spacebar preview is Twain's.

Do images inside the preview load?

Local relative images render in the app window but not yet in the Finder preview, a macOS sandbox limit we state rather than hide. Remote images are always blocked in previews, by design.

Does Quick Look work for MDX?

Yes. .mdx previews render with the same safe component handling as the app: known components become UI, unknown ones become labelled placeholders, and nothing executes.

Does previewing a file change it?

No. Viewing writes nothing: no sidecar, no history entry, no metadata. History and notes only ever record when you act on a document in the app.

This page describes what the app does today; when a capability is partial or pending, it says so. See how Twain compares to other Mac Markdown apps.

More capabilities

Markdown viewer MDX viewer Workspace and search All capabilities

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