Preview pane

Pressing A (or Enter / double-click) on a file opens a built-in preview to the right of the file list — one preview per tab. The pane takes a share of the window width, so it stays roomy for media and PDFs.

What it can preview

Text / code — scrollable.
Images — PNG, JPEG, GIF, WebP, BMP — width-fitted.
HEIC / AVIF / JXL — when an image converter is installed (sips ships with macOS; heif-convert, ImageMagick, or vips on Linux/Windows).
SVG.
HTML and Markdown — rendered as a static, no-JavaScript view (scripts never run, so a preview can’t do anything active).
PDF — paged.

For SVG, HTML and Markdown you can flip between the rendered view and the raw source with the header </> button (or X on a controller / F2). Markdown shows its original .md text, not the converted HTML.

Right crosses into the preview pane. B (or Escape) always closes it. What the other buttons do depends on the kind:

Text / image / SVG / HTML / Markdown — Up / Down scroll; A opens the file in the OS default app.
PDF — Up / Down turn pages; Home / End jump to the first / last page; A opens it externally.

When a file can’t be previewed

Binaries, unsupported formats, and oversized files can’t be previewed. DeckCrate offers to open them in the OS default app instead. From that prompt you can also press Y to pick a specific app (see Open file with…).

Open with the default app

You can open any file in its default application from the preview pane’s A button, or directly for any non-previewable file.

Open file with…

For a single highlighted file, the Open file with… entry in the command menu shows a controller-navigable list of installed applications, sorted alphabetically. A / Enter confirms, B / Esc cancels. It’s also offered as Y on the “can’t preview” prompt. Works on macOS, Linux, and Windows.