Quick Look Not Working on Mac? How to Fix It

You press the space bar and instead of a preview you get a blank window, a giant generic icon, or nothing at all. Quick Look runs as its own background service, and like any service it can wedge — usually after an app update, a huge file, or a misbehaving third-party preview extension. The fix is almost always one of the four steps below, and none of them touches your files. They work the same on Ventura, Sonoma, and Sequoia.

Fix 1: Restart the Quick Look service

Previews are drawn by a helper process called QuickLookUIService, not by Finder itself. When previews go blank mid-session, that process has usually hung. Kill it and macOS restarts it on demand:

# force-quit the preview service (it relaunches automatically)
killall -KILL QuickLookUIService

Open Terminal from Applications → Utilities, run the command, then select a file and press the space bar. If Terminal replies “No matching processes,” that's fine — it just means the service wasn't running, so move to the next fix. This command is read-only for your data; there is nothing to undo.

Fix 2: Reset the generators and clear the cache

Quick Look builds previews with per-filetype generators and caches the thumbnails it draws. A stale generator list or a corrupt cache produces exactly the “generic icon instead of a preview” symptom. Reset both with qlmanage, Apple's built-in Quick Look maintenance tool:

# reload all Quick Look generators
qlmanage -r

# wipe the thumbnail cache (it rebuilds automatically)
qlmanage -r cache

# then restart Finder so it uses the fresh server
killall Finder

The cache rebuilds itself as you browse, so the only side effect is that folder thumbnails take a moment to reappear the first time. Again, nothing here needs undoing.

Fix 3: Test the file, not the system

If only certain files fail, the problem may be the file type rather than Quick Look. You can ask qlmanage to preview a specific file from Terminal and show you what happens:

# open a test preview and print any errors
qlmanage -p ~/Documents/example.pdf

If that preview works but the space bar doesn't, the issue is Finder-side — log out and back in. If qlmanage also fails, the format needs a generator that's broken or missing. Previews for niche formats are supplied by apps, so reinstalling or updating the app that owns the format usually restores them.

Fix 4: Check third-party Quick Look extensions

Apps can plug their own preview extensions into Quick Look, and one crashing extension can take previews down for everything. Review what's installed:

1. On Ventura or Sonoma, open System Settings → Privacy & Security → Extensions → Quick Look.
2. On Sequoia, open System Settings → General → Login Items & Extensions, then find Quick Look in the Extensions list and click the info button.
3. Untick any extension you added recently — or all third-party ones — and click Done.
4. Test the space bar again. Re-enable extensions one at a time to find the culprit.

If previews only break after installing a specific developer tool or markdown utility, this is almost certainly the cause. A restart after toggling extensions helps macOS drop the old ones cleanly.

Still blank? The escalation path

If none of the four fixes lands, work down this list — each step rules out a layer:

1. Log out and back in. Cheaper than a restart and resets the per-user services Quick Look depends on.
2. Restart the Mac. Clears every cached service, including ones killall can't reach.
3. Check free disk space. Quick Look needs room to render and cache thumbnails; a nearly full disk breaks previews in odd ways. Keep several GB free.
4. Test in a new user account. Create one in System Settings → Users & Groups, log in, press space on a file. If previews work there, the problem is a preference or extension in your account, not macOS — go back to Fix 4 and be more ruthless.

Working previews in a fresh account plus broken ones in yours points the finger at third-party software nearly every time.

Once it's back, use it properly

Quick Look does far more than show a static preview — fullscreen slideshows, markup, and video trimming are all built in. See Quick Look on Mac: preview files without opening them for the full tour.