How to get the exact WebKit version when running self-built WebKit with native Safari?

Hi all, I'm new to WebKit. I have built up the WebKit with XCode based on the document. Now I run the WebKit with native Safari.app on my Macbook, so what I understand is that it will use my self-built WebKit instead of the native one in Safari.

Then how do I know that it truly do replace the default WebKit with my self-built one?

I check the default Safari with "what is my user agent" in Google, it says the AppleWebKit is 605.1.15. Then I do same check to my self-built WebKit, it still shows the AppleKit is 605.1.15.

So as the title goes, how do I get the exact WebKit version?

Thanks