Things that will make your website much faster

What will make my website faster? How to optimize page load time? How to make web site appear to load faster for end user?

Updated Feb 9, 2011.

This is excerpt from article: How big HTML images / CSS / JS / png / etc. should be to fit network packet (MTU) efficiently

List of things that will make your website much faster:

Server must support Keep-Alive. Otherwise change server / host / hosting company / etc. Do it NOW!
Reduce HTTP requests (CSS sprites, combine CSS, combine JS, inline CSS, inline JS)
Minifiy HTML, JS, CSS. Google Closure Tools, YUI Compressor, Minification
Gzip text/html, css, js (IE6 does not un-gzip CSS and JS, if reference is not from HEAD)
For IE 5 & 6 use gzip-only-text/html
Check if (Content-Encoding: gzip) then (Vary: Accept-Encoding) to allow cache both versions in proxy servers
CSS goes in head, JS goes at bottom – right before body closing tag
Defer JS if possible. Defer allows to load js after onload
Image formats: for photos – always use JPG, for everything else – PNG 8, for animations – GIF
Compress images: for JPG use ~~jpegtran or jpegoptim~~ Adobe Photoshop or Advanced JPEG Compressor (both non-free) or free GIMP, for PNG use OptiPNG or PNGOUT. I use non-free but the best one – PNGOUTWin
Think connections! Waterfall. webpagetest.org (probably the best site for web page speed / optimization test), Zoompf (a little overkill, but can be useful), Pingdom Tools
Try to serve assets in parallel, e.g, images.example.com, images2.example.com; subdomains can be on the same IP
Use 2-3 max 4 sub-domains
Optimize response headers, smaller, meaningful
Avoid redirects (301, 302, META refresh, document.location)
Remove ETAG
Use Expires + cache-control
25k and greater files are not cached on iPhone
Cache dynamic content PHP, ASPX, ruby etc.
example.com?param is not cached by most proxies
Serve static assets from cookie-less domain, like yimg.yahoo.com
After onload via js can pre-cache images (if you know where visitor will go next)
Can use double heads (if a lot of meta then put 2nd head at the bottom after closing BODY tag)
Use CDN if can afford

And remember about:

Validate HTML
Validate CSS
Validate RSS
Validate all 3 – HTML, CSS, RSS/Atom
Google Webmaster Tools
Test IE (Trident), FF (Gecko), Chrome & Safari (WebKit), Konqueror (KHTML), Opera (Presto), lynx :)
FF plugin — Html Validator
Firebug + Yslow! (Yahoo) + Page Speed (Google)
Aim for 99/100 both for yslow and pagespeed. It is possible!
sitemap.xml
robots.txt
favicon.ico (or will get many 404s)
apple-touch-icon.png (for iPhones)
If up-time is critical use website monitoring tool / service like pingdom.com

Related tools / links:

Apache module mod_pagespeed. Read more in Google Webmaster Blog about mod_pagespeed
To test if your website can handle x users. Website stress test (loadimpact.com).
GTmetrix – Analyze Performance
Yottaa – Monitoring & Scoring the performance Beta
Show Slow
Google Webmaster Guidelines
W3C Link Checker
Check and Visualize your RDF documents – RDF Validator