What Gatekeeper is
Gatekeeper is a security feature in macOS that checks apps before they are allowed to open. Its job is to make sure software comes from a trusted source and has not been tampered with, which helps protect your Mac from malware hidden inside downloads. Apple introduced it in 2012, and it now runs quietly in the background every time you open an app downloaded from the internet.
How it checks an app
When you open a downloaded app for the first time, Gatekeeper checks for a valid developer signature, a cryptographic seal showing who made the app and that it has not been altered since. It also checks whether Apple has notarized the app, meaning Apple's automated systems scanned it for known malicious content before release. Apps from the Mac App Store are reviewed by Apple and pass these checks.
The warnings you see
If an app fails these checks, Gatekeeper blocks it and shows a warning, for example that the developer cannot be verified or that the app may be damaged. These messages are designed to make you pause before running something unknown. Even for approved apps, macOS asks you to confirm the first time you open something downloaded from the internet, so you know it came from outside the App Store.
Opening an app you trust
Sometimes a legitimate app from a small developer is not notarized. If you are confident it is safe, you can allow it from the Privacy and Security section of System Settings, where an option to open it anyway appears after a blocked attempt. Use this carefully, and only for software from sources you genuinely trust, because bypassing the check removes an important layer of protection.
Part of a layered defense
Gatekeeper works alongside other macOS protections. XProtect scans for known malware signatures, and Apple can block software later if it turns out to be harmful. Together these layers mean that a single check is not the only barrier between you and malicious software. Keeping macOS updated matters here, since Apple refreshes these protections regularly with the latest threat information.
The bottom line
Gatekeeper is the Mac's first checkpoint for new software, confirming that apps come from identified developers and have been scanned by Apple before they run. Its warnings are worth taking seriously, and overriding them should be a deliberate choice reserved for software you trust. Combined with regular updates, it does much of the work of keeping everyday Mac use safe and worry-free.
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See also: What is the App Store? Explained, What is Xcode? Explained.
Sources
Published date reflects the original event date (2026-10-23). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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