Why and How Did We Use Browser Sniffing? For a long time browser sniffing was the way developers tested for various browsers and as a result used a different API or feature set. You can always manually detect by using the navigator.userAgent, but making sense of it can be difficult considering the vast amount of userAgent combinations. Some libraries were developed to assit the developer in making sense of the userAgent. A detect library can be found from QuirksMode and jQuery also provides the browser object with some sniffing information.