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

You just downloaded an app—maybe it's a utility for screenshots, a media converter, or something from GitHub. You double-click it, and instead of launching, you get this: 'The application can't be opened.' Or maybe it says '… is damaged and can't be opened.' Or '… cannot be opened because the developer cannot be verified.'

This usually happens right after you download something from the internet, but sometimes it also shows up after copying an app from another Mac or extracting it from a zip file. The trigger is almost always macOS Gatekeeper—Apple's security system that checks apps for a digital signature and a quarantine flag.

What's actually happening

When macOS downloads a file from the internet (Safari, Chrome, Firefox, any browser), it attaches an extended attribute called com.apple.quarantine. This is a hidden flag stored in the file system metadata. Gatekeeper checks this flag, and if it's set, macOS verifies the app's code signature against Apple's notarization service.

The error means one of three things:

• The quarantine flag is set, and the app isn't notarized. This is the most common case for open-source apps or older software.
• The app's code signature is invalid or missing—maybe the developer removed it, or something corrupted during download.
• The app is actually damaged (rare, but possible if the DMG or zip was truncated).

The reason step 3 works is that you're removing that quarantine flag manually. macOS then treats the app as if it were already on your Mac before you downloaded it, skipping the Gatekeeper check.

The fix: remove the quarantine flag

Open Terminal. You'll find it in Applications/Utilities or search for it via Spotlight (Cmd+Space).

1. Type xattr -cr (with a space at the end) into Terminal, but don't press Enter yet.
2. Drag the app (the .app file itself, not the DMG or zip) from Finder into the Terminal window. This pastes the full path.
3. Press Enter. You'll be prompted for your password if you're not on an admin account.

The full command should look like this:

xattr -cr /Applications/SomeApp.app

-c clears all extended attributes (including the quarantine flag). -r does it recursively, which matters because some apps have helper tools or frameworks inside their bundle that also carry the flag.

Now try opening the app again. If it still won't launch, or if you get a different error like '… is damaged', move on to the next step.

If that didn't work: check the code signature

Some apps need their code signature re-applied, especially after you modify the bundle (say, by removing languages or resources). You can check the current signature status with:

codesign -dv --verbose=4 /Applications/SomeApp.app

Look for the line that says Sealed Resources version or Authority. If you see code object is not signed at all, you can try signing it yourself with an ad-hoc signature:

codesign --force --deep --sign - /Applications/SomeApp.app

The - is a literal dash—it means 'ad-hoc signature', which creates a local signature without an Apple certificate. This tells macOS 'yes, this app is signed (by me)'. It won't pass notarization checks, but for local use it's enough to suppress the error.

I've had this work on a dozen different apps, from old open-source tools to something I built myself with Xcode that wasn't signed at all. It's not a perfect fix—some apps with hardened runtime won't run ad-hoc signed—but it's worth trying.

When you should just trash the app

If neither of those steps work, the app might actually be broken. A corrupt download happens more often than you'd think—especially with large files or unstable network connections. Redownload the app from the original source, making sure the download completes without errors. If the same error persists after a fresh download, the app itself is likely incompatible with your version of macOS.

For example, I've seen 32-bit apps that worked on Mojave fail with this exact error on Catalina and later, because Apple dropped 32-bit support entirely. No amount of quarantining or signing will fix that.

What to check if it still fails

Here's a quick checklist:

• Open System Settings > Privacy & Security. Scroll down to the 'Security' section. Do you see a message about the app being blocked? Click 'Open Anyway' if it's there.
• Check if the app is in a folder like Downloads or Desktop. Move it to /Applications. Some apps require being in the Applications folder to run properly—especially those that use sandboxing or helper tools.
• Verify the MD5 or SHA-256 checksum if the developer provides one. A mismatch means the file is corrupted.
• Reboot your Mac. I know it's cliché, but I've had Gatekeeper glitch out after a long uptime, and a restart cleared it.

If you're still stuck after all that, the app is likely not compatible with your macOS version. Check the developer's website for a newer version or an alternative.