MacDown Won't Open or Says "Damaged" on macOS: What to Do

MacDown won't open on a recent Mac because the original app hasn't been updated since January 2020. Its last stable build, 0.7.3, is not signed or notarized, so Gatekeeper blocks it with "Apple could not verify 'MacDown' is free of malware" or "MacDown is damaged and can't be opened". It is also Intel-only. The real fix is to install MacDown 3000, the maintained continuation, which is free and notarized. If you need the old app itself, click Open Anyway in System Settings ▸ Privacy & Security, or clear its quarantine flag with xattr.

Homebrew disabled the macdown cask on September 1, 2026, with the reason fails_gatekeeper_check, so brew install --cask macdown no longer works either.

I checked each fact here on November 5, 2026, on macOS 26.3, against the MacDown repository, the Homebrew API and Apple's documentation, and ran Gatekeeper's check on both apps myself. To compare MacDown 3000 with other apps rather than fix the old one, see the MacDown comparison.

What's wrong with the original MacDown#

The original repository's last push was in July 2023, and its last pre-release dates from February 2020. Gatekeeper trouble isn't new for it: users reported "MacDown is damaged and can't be opened" as far back as November 2019 (#1115). On an open issue from August 2026 (#1383), a reply points users to MacDown 3000.

On macOS 15 and later, the alert for an unsigned app reads "Apple could not verify 'MacDown' is free of malware that may harm your Mac or compromise your privacy".

Fix 1: install MacDown 3000 (recommended)#

MacDown 3000 calls itself "essentially MacDown Continued": it carries on the editor Tzu-ping Chung first published in 2014. It's free, MIT licensed, a universal app, and needs macOS 11 (Big Sur) or later. Gatekeeper accepted its 3000.0.8 build as "Notarized Developer ID" when I checked it, so it opens with no warning beyond the usual "downloaded from the internet" prompt.

Install it from macdown.app, or:

brew install --cask macdown-3000

Your .md files don't change: MacDown never had a proprietary format. If you still have the old app, drag it to the Trash afterwards so double-clicking a file doesn't pick the wrong one. To be sure, select a .md file, press ⌘I, choose MacDown 3000 under Open with, and click Change All.

Fix 2: open the original MacDown anyway#

If you need 0.7.3 itself, Apple documents the override for macOS 15, 26 and 27:

1. Download MacDown.app.zip from the 0.7.3 release, unzip it and move MacDown to Applications.
2. Double-click it once. macOS blocks it; close the warning.
3. Open Apple menu ▸ System Settings ▸ Privacy & Security, scroll to Security, and click Open Anyway. The button stays for about an hour after the blocked launch.
4. Enter your password. MacDown is saved as an exception and opens normally from then on.

Control-click ▸ Open, the shortcut older answers suggest, stopped working in macOS Sequoia.

If the alert says "damaged", the Open Anyway route may not be offered. Clear the quarantine flag in Terminal instead:

xattr -dr com.apple.quarantine /Applications/MacDown.app

I ran that command on a quarantined copy of 0.7.3 and checked that the flag was gone. If Terminal answers "option -r not recognized", a Python xattr is ahead of Apple's in your PATH: run /usr/bin/xattr -dr com.apple.quarantine /Applications/MacDown.app instead.

On Apple Silicon, macOS will then ask to install Rosetta 2, because MacDown 0.7.3 contains only Intel code. The MacDown 3000 comparison covers what that means for future macOS versions.

Is MacDown safe?#

MacDown is open source and was a popular editor for years; nothing suggests the 0.7.3 release is malicious. But an unsigned build gives macOS no way to confirm who built it or that it hasn't been altered since, and the app has had no security fixes since 2020. Apple's own guide warns that overriding these settings "is the most common way that a Mac gets infected with malware".

So: if you override, take the zip only from github.com/MacDownApp. Never take it from a download mirror. Better, use MacDown 3000, which gives you the same editor with a signature macOS can check.

If you only read Markdown#

Plenty of people kept MacDown around to read .md files, not to write them. For that, I built MacMD Viewer, so count me as biased here: it's a read-only viewer, signed with a Developer ID and notarized by Apple, that previews .md files in Finder with Quick Look, renders Mermaid diagrams, and reloads when your editor saves. It costs $19.99 once, before tax, and needs macOS 14 or later. MacDown 3000 stays the better pick if you write in it; MacMD Viewer vs MacDown has the side-by-side.

MarkText fails Gatekeeper for the same reason, with a different fix: MarkText won't open on Mac. The alert itself, across Markdown apps, is explained in Apple could not verify… is free of malware. If you're choosing a new editor rather than repairing this one, the MacDown alternatives roundup compares them.

Frequently Asked Questions#

Why won't MacDown open on my Mac?#

The original MacDown's last stable release, 0.7.3, dates from January 2020. Its app is not signed and not notarized, so Gatekeeper refuses it, and it is built for Intel only. Homebrew disabled its cask on September 1, 2026 for failing the Gatekeeper check.

Is MacDown safe to use?#

MacDown is open source and was a well-known editor, but the 0.7.3 build has no signature, so macOS cannot confirm who built it or that it has not been altered, and it has had no update since 2020. Download it only from the project's GitHub releases. For a maintained, notarized version, use MacDown 3000.

Is MacDown 3000 the same app as MacDown?#

MacDown 3000 is a continuation of MacDown by a different maintainer. It is free and MIT licensed, a universal app for Apple Silicon and Intel, and needs macOS 11 or later. Its Homebrew cask is macdown-3000.

Why does brew install --cask macdown fail?#

Homebrew disabled the macdown cask on September 1, 2026, with the reason fails_gatekeeper_check. Install MacDown 3000 with brew install --cask macdown-3000 instead.

Does MacDown run on Apple Silicon?#

The original MacDown 0.7.3 contains only Intel code, so it runs through Rosetta 2 on Apple Silicon. MacDown 3000 is a universal app and runs natively.

Sources#

All read or run on November 5, 2026: MacDown releases and issues #1106, #1115, #1383 · Homebrew API for the macdown and macdown-3000 casks · MacDown 3000 · Apple: Safely open apps on your Mac, Open a Mac app from an unknown developer, Updates to runtime protection in macOS Sequoia. Signature and architecture checks: codesign -dv, spctl -a -vvv -t exec and lipo -archs on macOS 26.3.