HTML/XHTML

• W3C HTML validator
• Web Design Group HTML validator
• HTML Tidy

CSS

• W3C CSS validator
• Web Design Group CSS Check

Accessibility

• WAVE
• Cynthia Says
• Functional Accessibility Evaluator
• Vischeck colorblindness simulator
• List of tools (WAI)

Hyperlinks

• Elsop LinkScan software
• Elsop LinkScan for CSU Libraries staff
• Xenu's Link Sleuth software
• W3C link checker online
• Web Design Group Link Valet online
• Firefox LinkChecker add-on
• Firefox OCLC LinkEvaluator add-on
• Chrome Check My Links

Readability and reading level

• Word
• Readability Plus
• SMOG
• JuicyStudio/Flesch-Kincaid

Spelling checkers

General

• Web Developer add-on
• Firebug add-on
• Firefox Total Validator add-on
• Check if a site contains malware
  

Browser Compatibility

Preview a site in multiple browsers
or versions of Internet Explorer

• Adobe BrowserLab
• Browsershots
• Spoon plugin
• IE NetRenderer
• IETester
• IE Tab for Firefox and Chrome

Mobile browsers

• http://en.wikipedia.org/wiki/Mobile_browser
• Firefox Mobile for Android
• Opera Mobile and Opera Mini for Android and iOS
• Dolphin Browser

Mobile emulators

Downloaded emulators give more realism than online simulators, but testing real devices is best.

• http://www.mobilexweb.com/emulators
• http://mobiforge.com/emulators/page/mobile-emulators
• The best mobile emulators and responsive design testing tools
• Adobe DeviceCentral
• Opera Mini online simulator
• Opera Mobile emulator
• Android browser emulator in the Android SDK