How can I check my web page for errors?

- General website and HTML checks use : W3C markup validation - CSS checking use : W3C CSS validation service - Speed test use this site its really fantastic service http://tools.pingdom.com/fpt/ - Accessibility use this : http://www.w3.org/services/html2txt?url=URL - Mobile-readiness use this : http://ready.mobi/launch.jsp?locale=en_EN - Analyze website of course the perfect site : http://www.google.com/analytics/ - Checking a Blog - Testing a sites usability you can use your own experince to check or use this site : http://fivesecondtest.com/

Errors may happen in any side of request cycle which includes: - Server side: each server has at least 2 logs, access log and error log, you need to check that log to see server side errors.
- Client side: which is javascript or jquery errors, which browsers have ability to catch such errors and view them to you, also you can use many tools and add-ones that helps you for describing such errors.
- Network side: this can be checked by HTTP response which can be covered also by addons on browser.

If you mean web application then there are two steps:1.
Backend : use log files and monitor them.2.
frontend(this is the hard one): use this code in each page window.onerror = function(message, url, linenumber) { sendToServer({message: message, line: linenumber, url: url}); }