macOS Gatekeeper Error — App Cannot Be Opened Fix

What Does This Error Mean?

macOS Gatekeeper blocks apps that are not from the Mac App Store or from identified (notarized) developers. When you see 'This app cannot be opened because it is from an unidentified developer' or 'Apple cannot check it for malicious software,' Gatekeeper is doing its job. This is a security feature — not a bug. For legitimate apps from trusted sources, there is a simple way to allow them to run.

Affected Models

MacBook Air
MacBook Pro
iMac
Mac Mini
Mac Pro
Mac Studio

Common Causes

The app was downloaded from the internet and is not notarized by Apple
The app is from a developer who has not paid for an Apple Developer account
The app's code signature was modified or damaged after download (possibly by a quarantine attribute error)
The macOS security setting is set to 'App Store only' which blocks all third-party apps
The app was created on an older macOS version before notarization was required

How to Fix It

Try right-clicking to open instead of double-clicking. Right-click (or Control-click) the app in Finder and choose 'Open' from the menu. A dialog will appear asking if you are sure — click Open.

This works for apps that are blocked but not for ones that macOS has detected as malicious. The right-click method grants a one-time exception.
Allow the app in Security settings. Go to System Settings > Privacy and Security. Scroll down to the Security section. After attempting to open the blocked app, a message appears there with an 'Open Anyway' button.

The 'Open Anyway' button only appears for about an hour after you attempted to open the app. If you do not see it, try to open the app again first.
Check your overall Gatekeeper setting. In System Settings > Privacy and Security > Security, confirm the setting allows apps from 'App Store and identified developers' rather than just 'App Store.'

If set to App Store only, legitimate third-party apps like Zoom, Spotify, and others will also be blocked.
Remove the quarantine attribute via Terminal if needed. Open Terminal and type: xattr -d com.apple.quarantine /Applications/AppName.app (replace AppName with the actual app name).

macOS adds a quarantine flag to all files downloaded from the internet. Removing it bypasses the Gatekeeper check for that specific file.
Verify the app is safe before bypassing. Research the app name and developer. Check that the download source is the official website. Avoid bypassing Gatekeeper for apps from unknown or suspicious sources.

Gatekeeper exists to protect you. Only override it when you are confident the app is legitimate.

When to Call a Professional

Gatekeeper blocks are rarely a professional service issue. However, if you are not sure whether an app is legitimate, do not bypass Gatekeeper — research the app and developer first. Only override Gatekeeper for software you trust.

Frequently Asked Questions

What is Gatekeeper and why does Apple use it?

Gatekeeper is a macOS security system that checks every app before it runs. Apple requires developers who want to distribute software outside the Mac App Store to register as Apple Developers and submit their apps for notarization — a process where Apple scans the app for malware. Gatekeeper verifies this signature when you open an app. If the app is not signed or notarized, Gatekeeper blocks it to protect you from potentially harmful software.

Is it safe to bypass Gatekeeper?

It can be safe, depending on the app. Many legitimate, well-known applications are distributed outside the App Store without full notarization — especially older apps and open-source tools. The key is to make sure you downloaded the app from the official source, not a third-party download site. If you downloaded it from a reputable official website, bypassing Gatekeeper is generally safe.

The app says it is damaged and cannot be opened. Is that different?

Yes. The message 'App is damaged and cannot be opened' is more serious. It can mean the app was genuinely corrupted during download, or it can mean macOS is blocking it for security reasons despite the different wording. Try re-downloading the app from the official source. If the message persists, try the xattr Terminal command described in Step 4 to remove the quarantine flag.