There are dozens of services available that are capable of checking your website for errors and finding ways of improving your 
General website and HTML checks
- W3C markup validation – The source to go to check HTML, XHTML or other markup language 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. You need a Google account to use these tools.
- Silktide Nibbler – 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 – Simple and easy to use online tool that allows you to identify any HTML errors you may have on your page.
- Feng-GUI – Great service that allows you to 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 – Fantastic service that displays any issues errors or compliance warnings you have with any CSS code.
- CSS Compressor – Although not a service to validate for errors this 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 the .CSS file and decrease the overall amount of bandwidth you use.
Speed test
- WebPagetest – Our favourite tool for testing a web pages load time.
- GTmetrix – Another fantastic tool for speed testing a web page as well as getting the optimised versions of images, pages, and scripts.
- Pingdom Tools – Fantastic service that gives you a good and easy-to-read overview of how long it takes for something to load on your web page. Keep in mind that most website visitors only spend a few seconds on each page they visit.
- WebSiteOptimization – Another great service to find how much time it takes to load your web page and what you can do to help decrease the overall time it takes to load it.
- Web Page Content Compression Verification – Great tool to test an individual page or element on the 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 – Great service that 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.
Accessibility
- Browsershots – Excellent online tool to test how accessible your web page is in all of the Internet browsers.
- Colorblind filter – Fantastic page to see how your page would look to someone who has colour blindness. This is an easy way to make sure that someone visiting your site, and has colour blindness, won’t miss something because your colour scheme is bad.
- HERA – Great page to verify if everyone regardless of any disability can view your page they may have.
- html2txt – A great method of converting your HTML page into a text document. This is helpful because many accessibility tools for the blind will convert pages to text. By using this tool, you can get a good idea how someone who’s blind may read your page.
- The Readability Test Tool – Quick and easy way to test the readability of your website and get a better idea about how many people would understand your content.
- IE NetRender – Great online service that allows you to see how your page is displayed in different versions of Microsoft Internet Explorer. This is really helpful if you need to test your web page in an older browser, such as IE6, which has compatibility and other issues with CSS.
Mobile-readiness
- mobiReady – By far the best site and service for checking how compatible your website or blog is when being viewed on a mobile device. This service not only gives you detailed information on why your website may or may not work, but also gives live demos on how the page will load on different mobile devices.
Analyse website
- Google Analytics – Fantastic free service offered by Google that gives you full details of the visitors visiting your website, what browsers they’re using, where they’re leaving, what they searched for, and much more. After making sure your website has no errors, having these services is always a good idea to help identify any other problems the above services may not have identified.
Checking a blog
If your page is a blog, consider using Is My Blog Working? to check and see if everything is operable. Is My Blog Working? can give you additional details about your page and assist you with changes and additions.
Testing a site’s usability
Having friends, family, and co-workers viewing your website is a great way to make sure your website not only works, but works on different computers. Other services like the UsabilityHub Fivesecondtest is also a great free way of testing the overall appeal of your site.
Source: Computer Hope
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