macOS 'The application can't be opened' error — the fix

Quick answer

Right-click (or Ctrl-click) the app in Finder and choose Open. Then click Open in the dialog that appears. That's it for 90% of cases.

Why does this happen?

macOS 10.15 (Catalina) and later enforce Gatekeeper more strictly than older versions. Every app downloaded outside the Mac App Store gets a quarantine attribute attached to it — an extended file attribute named com.apple.quarantine. When you double-click the app, macOS checks that attribute and, if the app isn't signed with an Apple Developer ID or notarized, it shows the error: “The application can't be opened.”

The reason the right-click trick works is that it bypasses the default Gatekeeper check for the first launch. It's not a security hole — it's the designed workflow for running unsigned software. Apple just made it less obvious than it used to be.

Step-by-step fix

1. Right-click (or Ctrl-click) the app in Finder. Don't double-click.
2. Choose Open from the context menu.
3. A dialog appears saying the app is from an unidentified developer. Click Open.
4. The app launches. You only need to do this once per app.

If that fails — meaning the dialog never appears or the app still won't launch — you've got a corrupted download or a more stubborn quarantine flag.

Alternative fix: Remove the quarantine attribute manually

Open Terminal (found in /Applications/Utilities/Terminal.app) and run:

xattr -d com.apple.quarantine /path/to/YourApp.app

Replace /path/to/YourApp.app with the actual path. A quick way: drag the app from Finder into the Terminal window after typing xattr -d com.apple.quarantine (note the space at the end). Then press Return.

This removes the quarantine flag directly. After that, double-clicking the app should work normally. The reason this works is that Gatekeeper checks for that attribute on launch. If it's gone, there's nothing to block.

When the app still shows as damaged or corrupted

Sometimes you get “The application is damaged and can't be opened.” This usually means the downloaded ZIP or DMG was corrupted, or the app was incorrectly bundled. Re-download the app from a trusted source. If it persists, verify the app's code signature:

codesign -dv /path/to/YourApp.app

Look for adhoc in the output — that means the signature is invalid. The app is genuinely broken. Delete it and download again.

Prevention: How to avoid this in the future

Two things will stop this from happening again with new apps:

• Download from the Mac App Store — all apps there are notarized and signed. No gatekeeper issues.
• If you must download outside the store, check the developer's website. Reputable developers sign their apps with Apple Developer IDs. The error won't appear for those.

Also, if you're a developer distributing your own app, sign it properly: get a Developer ID certificate from Apple's Developer Program, use codesign --deep --force --sign, then notarize it with xcrun notarytool. That's the cleanest path.

One more thing: macOS 10.15 and later also require a hardened runtime. Without it, even correctly signed apps might trigger the error. If you control the app, check that the hardened runtime entitlement is enabled.