How it works
No Terminal required. Drop a file, pick a handler, confirm the side effects.
Drop or choose a file
Any type — Markdown, PDF, images, code, whatever Spacebar is getting wrong.
See who claims it
Doctor lists the Quick Look extensions that register for that file’s type, and probes which one is actually serving the preview.
Prefer one handler
Pick the extension you want. Confirm which peers will be ignored, apply the repair, and Undo if you change your mind.
Browse all extensions
The Extensions tab shows every registered preview plugin with Use / Ignore / Default controls.
What you get
File-first diagnosis
Works for any UTI or file type — not just Markdown.
Prefer + ignore with Undo
Confirmations list every affected handler before anything changes.
Active-handler probe
Briefly invokes Quick Look to see which extension is serving Spacebar. A quick flash is expected.
Extensions inventory
Use, Ignore, or Default any registered preview extension.
Copyable diagnostic report
Share a plain-text report with support when you’re stuck.
Automatic updates
Sparkle checks for new builds after install. No App Store required.
Worth knowing
- Ignore is all-or-nothing per extension. macOS has no per-file-type preference API, so ignoring an extension turns off its previews for every type it supports — not just the one you’re diagnosing.
- Doctor doesn’t silently disable anything. Every ignore is listed and confirmed before it’s applied, and the most recent repair can be undone with Undo last repair.
- Doctor may briefly flash a Quick Look window while probing which extension is serving a file’s preview. That’s expected — Doctor closes it automatically.
- Detection is best-effort. Absence of a detected process doesn’t prove an extension is unused, and the probe can differ from Finder’s Spacebar preview in rare cases.
Related to Marked Quick Look — not the same app
Marked Quick Look is a paid Mac App Store preview extension that renders Markdown in Finder. Quick Look Doctor is a separate free utility that diagnoses and repairs Quick Look handler conflicts for any file type — Marked QL included when it's one of several claimants.
Doctor does not make Marked “win forever,” and it doesn't silently kill peer extensions. You choose a preferred handler; confirmations name what else gets ignored.
Marked Quick Look's in-app Diagnose (coming in 1.0.5) may deep-link here when a richer repair tool is the better next step.
Download & install
- Download
QuickLookDr.zip - Unzip and move Quick Look Doctor.app to
/Applications - Launch it once
Updates check automatically via Sparkle after install. Developer ID signed and notarized — not distributed through the Mac App Store.
Frequently asked questions
- Do I need Marked or Marked Quick Look to use Quick Look Doctor?
- No. Quick Look Doctor is a standalone free utility. It works with any Quick Look extensions on your Mac, including Marked Quick Look if you have it installed.
- Is Quick Look Doctor free?
- Yes. It’s a free, notarized direct download for macOS 13.0 or later. Not sold on the Mac App Store.
- Does it only fix Markdown?
- No. Drop any file type. Doctor diagnoses claimants for that file’s UTI and can prefer one handler over the others.
- Will ignoring an extension break other file types that extension handles?
- Yes — ignore is all-or-nothing for that extension. For example, ignoring Highland also affects Fountain and textbundle previews that Highland provides. Confirmations list what else each peer handles when known.
- How is this different from the Marked Quick Look troubleshooting Terminal commands?
- The troubleshooting page walks through pluginkit by hand. Doctor runs those same PluginKit controls in a GUI: drop a file, see claimants, prefer one handler, ignore peers with confirmation and Undo — no Terminal spelunking required.
Still stuck after a repair? Email marked@brettterpstra.com with Doctor's diagnostic report, or work through the Marked Quick Look troubleshooting guide.
Bundle ID: com.brettterpstra.QuickLookDoctor · Sparkle appcast