Free SEO Tools

Website page size, speed test & performance monitoring tools

  • www.websiteoptimization.com
  • tools.pingdom.com
  • www.gtmetrix.com

Domain look up tool

  • www.domaintools.com (Note: Useful for server location, server IP, reverse IP, etc.)

Free backlink analysis tools

  • www.backlinkwatch.com
  • www.opensiteexplorer.org

Broken link discovery tools

  • www.iwebtool.com/broken_link_checker
  • validator.w3.org/checklink
  • Xenu Link Sleuth - it's actually a software package you need to install on your PC

HTML source code error detection tool (a.k.a. HTML validator)

  • validator.w3.org

XML Sitemap generation tools

  • www.web-site-map.com
  • www.xml-sitemaps.com

Advanced SEO Tools:

Clean up your Web pages with HTML Tidy (Google recommended). Quickly and easily clean up your code with the click of a button.
http://www.paehl.de/tidy/

SEO Toolkit from Microsoft

http://www.microsoft.com/web/seo/

Screaming Frog SEO Spider Tool

Website Crawler software useful to discover issues related to links, images, CSS, script and other onsite SEO elements.
http://www.screamingfrog.co.uk/seo-spider/

Handy SEO addons for Chrome:

SEO quake - Click here
SEO for chrome - Click here
Meta SEO Inspector - Click here

Some Other Non-SEO Tools

Paste Tool - www.pastebin.com
Find similar websites - www.similarsitesearch.com