When working on some web site application it is obvious to improve website performance. In any website performance network time is very important factor and now days web application are using a lot of resources like images, css, js and others.
To check what resource is taking how much time and what is blocking time, http status code to validate every resource is working fine(200 and 304), what are brocken resources (404..). There are many tools and methods are available to do this. Google Chrome web browser is also capable to do these verification efficiently.
Using Chrome developer’s tool network option one can check and verify websites very easily. To use this launch developers tool using F12 key and load or reload website page. Chrome browser developer’s tool will show you results.
In logs first you need to fix all 404 status code call’s either in web page or your server application. Resource not found hampers performance.
After fixing all 404’s you need to check which call is taking more time and you should try to reduce time by compressing that resource. You can also combine css and js to reduce no of request’s.
You should try to include js and css under the fold.