2019 UPDATE! - Many fixes, detailed list of header tags, improved video detection, and introducing UI translations in italian, spanish and japanese, JSON-LD, large images detection, resource hints tags and more.
Please give me feedback about translations, more are coming.
Meta data is not just the usual HTML meta tags, but the XFN tags, various microformats, the recently introduced canonical attribute, the no-follow links and so on.
This extension is mainly aimed at web developers that need to verify the HTML of their site to follow the Webmasters' Google Guidelines, but even to who is curious about any page contents that are usually not visible, but can reveal interesting site properties.
Alerts are showed when the meta data is not within certain ranges, for example when the description tag is too short, or too long.
There are links to info-sites ( mainly SEO-oriented ) pointing to the exact page about the site you are watching. Feel free to request new links, I'll add only the good ones (there are many sites all showing the same data).
Anyway, in one of the next updates, the links list will be customizable.
2.1.7 - Introduced tooltips in UI, detailed list of header tags, more H1 tips, fixed issue with with twitter description containing html tags, initial japanese translation
2.1.6 - fixed video links - styles fix - handled yandex-verification, ahrefs-site-verification, p:domain_verify and bitly-verification - fixed issue in detecting large images - new CMS section - new Mobile section
2.1.5 - resource hints area - handled baidu-site-verification
2.1.4 - large images detection - fixed issue with JSON-LD - styles fix
2.1.3 - JSON-LD recognized
2.1.2 - layout improvements - video link discovery - fixed rare issues with malformed meta tags - keywords info - italian and spanish translation
2.1.1 - video tag discovery and download - layout improvements - online-tools cleanup
2.1.0 - improved page title detection - code optimizations - showing "alternate", "shortcut icon", "icon" and "archives" link tags - Added APP LINK section - increased the max description length to 230 - minor layout fixes - new about section - missing keywords meta tag is not a warning anymore
2.0.9 - minor fixes
2.0.8 - moved "robots" in common tags - added "geo" group - GoogleMaps(tm) links for location data - IMG tags report and warning for missing ALT attribute.
2.0.7 - OpenGraph checker - tools added: Norton Safe Web, GPlus Ripples explorer - minor fixes.
2.0.6 - fixed case-sensitive issues - layout improvements - meta data is now grouped in "common", "opengraph", "twitter", "schema.org" and "other" - the pop-up reopens on the last used section - added check for invalid "value" attribute
2.0.5 - no follow highlight is back - options page, good for future additions! - added more social verification tools - added Nibbler too
2.0.4 - Restored and updated the "on-line tools" section - layout fixes
2.0.3 - small fix with missing meta content - 5 stars rating for HTML check - layout fixes - badge refresh - doctype fix
2.0.2 - added html, h1, h2 tags check.
2.0.1 - small fix
2.0.0 - rewrited to new guidelines - added rich snippets data - more warnings - moved data to popup
1.8.3 - Style fixes, speed improvements, basic HTML5 report.
1.8.2 - Added favicons to external scripts URLs, added links to tags explanations. Bugfixes.
1.8.1 - Google Profiles are now detected and fully listed in the Page Details (found on the icon menu)
1.8 - Added more unique prefixes to css classes, "always white text" fixed, custom font size, explained "description too long/short" values, removed "show visited links" it is not working anymore due to security issues, fixed head title (added warning and length count),
improvements to the printable "page details", checked various sites for layout issues
1.7.10 - Fixed graphics issues, visible in latest Chrome Dev
1.7.8 - Added the requested close button, and "Rich Snippets Testing Tool","Copyscape Plagiarism Checker","Keyword Density Analyzer" tool links
1.7.7 - Basic RDFa implementation.
1.7.6 - Graphic enhancements
1.7.5 - Fixed some tool links, edited some icons, added "content-language"
1.7.4 - Cleaned script tags, details page has more data, password safety warning, fixed font styles, meta links are clickable, linked images are showed, speed improvements.
1.7 - Added a printable details page, accessible from the popup options.