The majority of WordPress themes and their details can be detected, but there are a small number of sites that may have their theme hidden for various reasons either for security or because they are a customized theme.
Note that this tool will detect if a site is running Drupal or Joomla instead of WordPress.
Yes, should work for all WordPress versions from 2.x through to the most current WordPress release.
If you want to check the homepage, then just the domain is fine, otherwise you need to specify the full URL or the page you wish to check. Note that some websites run a WordPress blog off their main non-WordPress site, so in these instances, ensure you specify the URL to the blog, eg: http://example.com/blog
Also, some plugins may only be active on a particular page/post (eg: commenting plugin), so specifying the URL will give you more information specific that that URL.
In the Top 10 WordPress Themes report, the themes are consolidated by the theme provider. For example, WooThemes have a lot of individual themes that all come under the WooThemes framework, so rather than dilute the statistics, they are all counted as WooThemes.
Due to the nature of the way some plugins operate, it isn't possible to list every single plugin that is active on a site.
A lot of WordPress plugins are effectively invisible as they work behind the scenes or are for admin purposes.
This site was created in early 2011 to answer the many forum requests asking "What WordPress Theme Is That?" It came well before a series of copycat sites were created.
The design and programming was developed by Ultimate Marketing Strategies.