Great question @DevKumar
On internet there are numbers of online tools, where you can check it out your website speed and their inside bugs or errors. Most prominent tool name is Google PageSpeed Insights which analyze each server file, CSS style-sheets, compressed or uncompressed files, website responsive layout and much more.
Another one is Pingdom tools and GTmetrix, both are recommended and have multiple option to measure your website current status.
Hopefully, the answered is your question.