Important Note (Disclaimer):

Disabling the Gatekeeper is not harmful to your macOS alone but if you disable the Gatekeeper and run an infected or a malicious software it might put your computer’s safety at risk. Please use the Gatekeeper Toggler if you know what you are doing. We won’t be responsible if you damage your OS and/or your files and your system’s security if you run a malicous software once the Gatekeeper is disabled.

We strongly suggest that you enable the Gatekeeper once you completed the task that required the Gatekeeper to be disabled.

Gatekeeper Toggler doesn’t contain any viruses or malware, it just simply runs the commands for disabling or enabling the macOS’s Gatekeeper.

What is Gatekeeper?

Gatekeeper is a new feature which was introduced in macOS Lion 10.7.5 and above that builds on OS X's existing malware checks to help protect your Mac from malware and misbehaving apps downloaded from the Internet.

The safest and most reliable place to download and install apps is via the Mac App Store. Apple reviews each app before it's accepted by the store, and if there's ever a problem with an app, Apple can quickly remove it from the store.
For apps that are downloaded from places other than the Mac App Store, developers can get a unique Developer ID from Apple and use it to digitally sign their apps. The Developer ID allows Gatekeeper to block apps created by malware developers and verify that apps haven't been tampered with since they were signed. If an app was developed by an unknown developer—one with no Developer ID—or tampered with, Gatekeeper can block the app from being installed.
Note: If you have an app that has not been signed with a Developer ID to support Gatekeeper, contact the developer of the app to determine if they offer an update which supports Gatekeeper.

But some times for you might need to turn off the Gatekeeper to install or run an application that is not downloaded from AppStore or developed by an unverified developer and Gatekeeper Toggler will help you to easily turn of the Gatekeeper in order to run those applications, you can also use the this app to turn it back on.

You can read the complete article at:
https://support.apple.com/en-us/HT201940

Why do I need to disable the Gatekeeper anyway?

This message doesn’t necessarily mean that the application is damaged to it is infected by a malware, the Gatekeeper cannot simple identify the package signature which might be due to a really damaged file or just the signature of the file is invalid according to macOS.

If that’s the case and you are sure that the package is healthy and you decide to install it anyway you need to disable the Gatekeeper to continue, so that’s where you can use the Gatekeeper Toggler to easily disable the Gatekeeper.

Once you successfully installed your app you can easily turn the Gatekeeper back on.

When the Gatekeeper is turned off you will be prompted with another message that look like this:

All you have to do is to click on the “Open” button and the application installer will open.

When the Gatekeeper is On and you want to turn it off:

When the Gatekeeper is on you will be prompted to disable it if you want and you can click “Disable” button which will ask you for administrator password just to make sure that you have the privilege to disable it.

If you do not have the administrative privilege or you don’t want to disable the Gatekeeper just simply click “Exit” and the application will close without making any changes to your current settings.

When the Gatekeeper is Off and you want to turn it on:

When the Gatekeeper is off you will be prompted to enable it by clicking the “Yes” button which will ask you for administrator password just to make sure that you have the privilege to enable it.

If you do not have the administrative privilege or you don’t want to enable the Gatekeeper just simply click “No” and the application will close without making any changes to your current settings.