> For the complete documentation index, see [llms.txt](https://debugme.gitbook.io/project/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://debugme.gitbook.io/project/master.md). # The Performance Book We can improve performance in the following places: ### Frontend Processing #### What are the parts of the ***critical render path*** * Browser requests HTML page * Browser starts building DOM as it parses HTML * Browser finds *\* tag in HTML so requests CSS file * Browser starts building CSSOM as it parses CSS * Browser finds *\ ``` #### JS * Load scripts asynchronously (*Use for scripts that don't affect DOM or CSSOM e.g. Google Analytics*) * Defer loading of scripts (*Use for scripts that affect DOM or CSSOM for below the fold content*) * Minimise DOM manipulation * Reduce long running scripts ![](/files/-LN6e56ou84zouKoWc8z) ### Network Processing #### How long it takes for data to go up/down the wire * File Size - make sure files being requested are as small as possible * Shrink the size of your CSS files: * Shrink the size of your HTML files: * Shrink the size of your JS files: * Shrink the size of your IMG files: * Scrub metadata from from your IMG files: * Prefetch files likely to be used soon: * Consider max connections per domain for fetching files: * Use profiling tools to find out what needs to be optimised: * page weight calculator: * page speed insights: * File Count - make sure as few files are being requested as possible * Above the Fold - make sure only ATF assets requested in \ and lazy-load below the fold assets in \