There are dozens of services available that are capable of checking your website for errors and finding ways to improve various webpages. Below is a listing of some of our favorite free online services.
General website and HTML checks
CSS checking
Speed tests
Accessibility
Mobile-readiness
Analyze website
Checking a blog
Testing a site’s usability
General website and HTML checks
W3C markup validation - The official validator of the World Wide Web Consortium. An invaluable resource for checking HTML, XHTML or other markup languages you use on your web page for errors.
Google Webmaster Tools - A must for any Webmaster. With this free service, you can identify any page or links with errors, scan for malware, find pages with short or missing titles, find duplicate meta tags, and much more. It should be noted that you’ll need a Google account to use these tools.
Silktide Nibbler - A fantastic free online service that gives you a good complete overview of your website with an overall score.
Woorank - Another fantastic free online tool that gives you a quick and easy-to-read overview of problems you may have on your site.
HTML Tidy - A simple and easy-to-use online tool that allows you to identify any HTML errors you may have on your page.
Feng-GUI - Upload a picture of your homepage or other pages and generate a heat map of where the visitor’s eyes are most likely to go first.
CSS checking
W3C CSS validation service - Displays any issues errors or compliance warnings you have within any CSS code.
CSS Compressor - Although this service cannot check for errors, it is a great tool to use after your CSS code has been verified. Using this tool, you can shrink your CSS file to help the overall load time of every page that links to it, as well as decrease the overall amount of bandwidth you use.
Speed test
WebPagetest - Our favorite tool for testing a web pages load time.
GTmetrix - Speed test a web page as well as optimize versions of images, pages, and scripts.
Pingdom Tools - A fantastic service that gives you a good and easy-to-read overview of how long it takes for something to load on your webpages. Keep in mind that most website visitors only spend a few seconds on each page they visit.
WebSiteOptimization - A service used to find how much time it takes to load your web page and what you can do to help it load faster.
Web Page Content Compression Verification - Test an individual page or element on a page (such as a .CSS or .JS file) to see if it’s being compressed before being sent using gzip.
Global load time performance test - Test your web page load times around the world.
HTTP archive - Provides the complete history of the speed of a website that can go back several months.
Load Impact - A great online test for verifying your website will perform well under high traffic volumes.
WhichLoadsFaster - If you’re updating or revising a website, this is a great place to quickly test and compare the load times between two different pages.