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Getting Started
Up and running in under a minute.
Launch MarkPeek once after installing — that registers its Quick Look extension with macOS. From then on there’s nothing to keep open: select any Markdown file in Finder and press the space bar to see it rendered. MarkPeek works on the desktop and in the column-view preview pane too.
Frequently Asked Questions
Quick answers to common questions about MarkPeek.
I installed MarkPeek but nothing changed. What now?
Open the MarkPeek app once after installing — that’s what registers the Quick Look extension with macOS. Then select a .md file in Finder and press space. There’s no window to keep open; the app just needs that first launch.
How do I turn the preview on or off?
Quick Look extensions are managed by macOS in System Settings → General → Login Items & Extensions → Quick Look. MarkPeek appears there once you’ve launched the app, and you can toggle it whenever you like.
Which Markdown files does it preview?
Common Markdown files such as .md and .markdown. MarkPeek supports CommonMark plus GitHub-Flavored Markdown features like tables, task lists, and strikethrough.
Does the preview have a footer or watermark?
No. MarkPeek renders your document cleanly — no footer, no watermark, no branding added to the preview. That’s the whole point.
Why don’t images in my Markdown show up?
Quick Look extensions run in a strict sandbox and are only given the file you’re previewing — not the other files it links to. So images referenced by a local path can’t be loaded, and MarkPeek shows their alt text instead. Everything else renders normally.
Does MarkPeek change my files?
Never. MarkPeek is read-only — it reads the file solely to render the preview and makes no changes to your documents.
Is it really free?
Yes. MarkPeek is free, with no in-app purchases and no subscription.
How do I remove MarkPeek?
Drag the MarkPeek app to the Trash, just like any other app. The Quick Look extension lives inside the app, so deleting the app removes the preview feature automatically.
Does deleting the app leave anything behind?
Around 50 KB of settings — your chosen appearance and text size — which is how it goes for nearly every Mac app. macOS keeps a sandbox folder for each app it has run, under ~/Library/Containers/ and ~/Library/Group Containers/, and leaves it there in case you reinstall. MarkPeek adds nothing beyond that: no login items, no background process, no helper tools, nothing outside its own folder.
To clear it as well, delete the folders starting com.doncastle.MarkPeek in those two locations. A sandboxed app can’t delete its own container on the way out, so this is macOS housekeeping rather than anything MarkPeek chooses.
What macOS version do I need?
MarkPeek requires macOS 26 or later.
Developer Notes
Things worth writing down, found while building MarkPeek.
Where Quick Look can and can’t reach
Found September 2026, building MarkPeek on macOS 26.
A Quick Look extension doesn’t get free run of the disk. macOS hands it the single file you selected and nothing else, and that boundary is stricter than it first appears. Two cases came up during development:
Files a document references. If a Markdown file links a local image, the extension is never given that image — only the document. Reading it fails with a permission error even though the file sits right beside it and you own it. Inlining the image as a data URI doesn’t help either, because that still requires reading the bytes first. This is why MarkPeek shows an image’s alt text rather than a broken icon.
Other apps’ sandbox containers. An app’s
private container —
~/Library/Containers/<app>/ — is readable
only by the app that owns it. Not by other apps, not by Quick Look
extensions, and not even by you from Terminal, which returns
Operation not permitted. MarkPeek’s first
“Try it” button wrote its sample to the app’s own
temporary directory, which lives inside that container — so
the file appeared in Finder but could never be previewed. The fix
was to save the sample where the user chooses instead. The same
protection applies to
~/Library/Group Containers/.
Ordinary locations are fine: Desktop, Documents, Downloads, external drives, anywhere you normally keep files. The rule of thumb is that Quick Look works on files you can select in Finder, and stops at anything owned by another app’s sandbox.
Contact Us
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Email Support
For support, bug reports, or feature requests, send us an email and we’ll get back to you.
[email protected]App Information
App Name: MarkPeek
Platform: macOS 26+ (Mac)
Type: Quick Look preview extension