Updated November 26th, 2019.
Sometimes you download a Mac app and it won’t open. You get a dialog box that says the app can’t be opened because it’s from “an unidentified developer” and your security settings won’t allow it.
Apple has a security feature called “Gatekeeper” which protects your Mac from malicious apps. Gatekeeper requires apps to either be from the Mac App Store (a place that Apple controls) or from a developer who is registered with Apple. Apps that don’t meet the requirement will not launch, at least not without a little bit of work (which is what this article is about). I’ll show you what to do in a minute. But first, a little more background.
Gatekeeper’s protection, unfortunately, can also block good apps– apps that were written by someone who didn’t belong to Apple’s Developer Program when the app was written, or apps that were written before these requirements were put in place.
Older Mac systems allowed you to change your Mac’s Security & Privacy settings to allow any app to run, but that options been removed. In macOS 10.12 and higher, your choices are “Allow apps downloaded from Mac App Store” and “Allow apps downloaded from Mac App Store and identified developers.” See the screenshot below.
Now, if you look around the internet, you’re sure to find instructions for changing your Gatekeeper security settings via the Terminal so that any app will open. I wouldn’t do that– if you do, you’re asking for trouble, and this is trouble Apple went to pains to protect you from. Instead, the thing to do is to leave your Security settings alone, and to grant permission to apps on a case by case basis.
It’s easy: just hold the Control key down and click on the app that won’t open. You’ll get this menu:
Choose “Open” (the very first item in the menu, at the top) and you get this box. It looks a lot like the one you got when you double-clicked the app, but it’s not the same:
The first box (the one at the top of this blog post) said the app couldn’t be opened. This box asks whether you’re sure you want to open it or not. If you know where you got it, and you trust the source, you can click the Open button. Note that it is not the default button choice– you have to click the “Open” button. As soon as you do that, the app opens.
One cool thing: you only have to do this once per non-authorized app. The Mac will remember that you granted the app permission to launch, so from then on you just double-click it, like you do with the rest of your apps.
In macOS 10.14 (Mojave) you get another way to launch an app from an unidentified developer: the General tab of the Security & Privacy preference pane. So, after seeing this:
… you can go to System Preferences (under the Apple menu), and then go to Security & Privacy and see this:
The result is the same either way– the app opens, and from then on it won’t complain about being from an unidentified developer.