Can somebody explain to me why Googles result using their own service page speed insights versus the api gives me different result? This site scores 100/100 using to online tool but when testing the same site using command line it only scores 99/100? I know this is a not a big deal and I'm not looking to score 100/100 but i'm just curious why they give two different result from the same service?
PageSpeed rules and weights for each are changing all the time, based on new data, or improvements in the underlying algorithm. At different points in time, the online tool and the API may use slightly different versions - either because one is out of sync, or we're experimenting with a different set of rules. Hence the discrepancy.. This also applies to the PageSpeed extensions for FF and Chrome.