Fix: "App" can't be opened because Apple cannot check it for malicious software. (macOS Gatekeeper Error)

TL;DR Quick Fix

If you trust the application and just need to open it quickly, the fastest way to bypass Gatekeeper for a single launch is by using the contextual menu:

Locate the application in your Applications folder or Finder.
Control-click (or right-click) the application icon.
Select Open from the contextual menu.
A dialog will appear asking if you're sure you want to open it. Click Open.

This method usually adds an exception for the application, allowing you to open it normally from then on.

Understanding the Gatekeeper Block

You've encountered the error:

"App" can't be opened because Apple cannot check it for malicious software.

This message means macOS's security feature, Gatekeeper, is preventing the application from launching. Gatekeeper's role is to help protect your Mac from malware and potentially harmful applications by verifying software before it runs.

When you download an application from the internet that isn't from the Mac App Store or isn't signed by an identified Apple developer, Gatekeeper flags it as coming from an "unidentified developer." This is a security measure. macOS doesn't know if the application is safe because it hasn't been notarized by Apple. For legitimate applications from smaller developers or open-source projects, this is a common hurdle.

Fix Approaches

Here are several ways to fix this Gatekeeper block, ranging from temporary bypasses to more permanent solutions, depending on your needs and your macOS version.

Method 1: Open with Control-Click (One-Time Bypass)

This is the same as the TL;DR quick fix and often the simplest solution for a single application you trust. It creates an exception for that specific app.

Find the app in Finder (usually in your Applications folder).
Control-click (or right-click) the app icon.
From the menu that appears, select Open.
You'll see a warning dialog. Click Open again to confirm.

The application should now launch, and you won't typically see this warning again for that specific app.

Method 2: Adjust Security & Privacy Settings (Older macOS or Post-Block)

The options available in System Settings/Preferences have changed over different macOS versions. Here's what to look for:

For macOS Ventura (13) and later:

The "Allow apps downloaded from" options are more restricted. You won't find an "Anywhere" option.

If you've already tried to open the app and it was blocked, go to System Settings > Privacy & Security.
Scroll down to the Security section.
You should see a message like "'App Name' was blocked from opening because it is not from an identified developer." Next to it, there will be an Open Anyway button.
Click Open Anyway. You'll be prompted to confirm.

For macOS Monterey (12), Big Sur (11), Catalina (10.15):

Go to System Preferences > Security & Privacy.
Click the General tab.
Click the lock icon in the bottom-left corner and enter your administrator password to make changes.
If you've already tried to open the app and it was blocked, you'll see a message like "'App Name' was blocked from opening because it is not from an identified developer." Next to it, click Open Anyway.

For macOS Mojave (10.14) and earlier (where "Anywhere" option might exist):

In older macOS versions, there was an option to allow apps from "Anywhere." This option was removed in macOS Catalina for security reasons.

Go to System Preferences > Security & Privacy.
Click the General tab.
Click the lock icon and enter your administrator password.
Select the radio button next to Anywhere under "Allow apps downloaded from:"

Warning: Enabling "Anywhere" significantly reduces your Mac's security by allowing any application to run, regardless of its source or developer signature. Use this option with extreme caution and consider reverting it after installing trusted software.

Method 3: Use Terminal to Remove Quarantine Attribute (Recommended for Specific Apps)

Applications downloaded from the internet (especially via browsers) are marked with a "quarantine" extended attribute (com.apple.quarantine). Removing this attribute tells Gatekeeper to treat the app as if it originated from a trusted source, allowing it to run.

This method is safer than completely disabling Gatekeeper as it only affects the specific application you target.

Open Terminal (found in /Applications/Utilities/).
Use the xattr command to remove the quarantine attribute. Replace /path/to/App.app with the actual path to your application. You can drag and drop the application from Finder directly into the Terminal window to get its full path.

sudo xattr -cr /path/to/App.app

For example, if your app is named "MyCoolApp.app" in your Applications folder:

sudo xattr -cr /Applications/MyCoolApp.app

You'll be prompted for your administrator password.

The -c flag clears all extended attributes, and -r applies it recursively to all contents within the app bundle. This is a very effective way to bypass Gatekeeper for a specific app.

Method 4: Use Terminal to Temporarily Disable/Enable Gatekeeper (Advanced/Last Resort)

This method completely disables Gatekeeper for all applications. It's generally not recommended for everyday use due to security implications, but it can be useful for troubleshooting or for advanced users who fully understand the risks.

Check Gatekeeper Status:

spctl --status

You'll see either assessments enabled (Gatekeeper is on) or assessments disabled (Gatekeeper is off).

Disable Gatekeeper:

sudo spctl --master-disable

Enter your administrator password when prompted. After running this, the "Anywhere" option might reappear in System Settings/Preferences > Security & Privacy > General on some macOS versions, or it will simply allow unsigned apps to run.

Strong Warning: Disabling Gatekeeper leaves your Mac vulnerable to unsigned and potentially malicious software. Only use this if you absolutely understand the risks and intend to re-enable it immediately after installing trusted software.

Enable Gatekeeper (Highly Recommended After Disabling):

sudo spctl --master-enable

Always re-enable Gatekeeper as soon as you've successfully launched your desired application to restore your Mac's security.

Verification Steps

After applying any of the fixes:

Try to open the application normally by double-clicking its icon in Finder.
If the fix worked, the application should launch without displaying the Gatekeeper warning.
If the application still doesn't open, double-check that you applied the correct path in Terminal commands, or try a different method.