"Checkpoints
Accessibility - check WCAG and Section 508 guidelines against many file types: find flashing GIFs, untagged PDFs
Broken Links - check for broken links and spelling errors
Compatibility - check for HTML, script and image formats that don't work in common browsers
Search Engine Optimization - check Google and Bing webmaster guidelines
Privacy - check for compliance with EU and US law
Web Standards - validate HTML and CSS
Usability - check against Usability.gov guidelines"
Twitter cards make it possible for you to attach media experiences to Tweets that link to your content. Simply add a few lines of HTML to your webpages, and users who Tweet links to your content will have a "card" added to the Tweet that’s visible to all of their followers.