Our mission is to provide an easy way to check web pages in large sites.
Say, for example, you have a site with 1,000 web pages and you want to check HTML and A11Y on each page - instead of doing 2,000 manual checks just give us a starting URL and we'll visit it to discover its internal pages, and validate each of them.
Rocket Validator is therefore basically a web spider and a reporting interface, but the real checking of your pages is done using the W3C Validator and the axe-core accessibility engines, hosted on our own servers. We don't decide what is considered a validation issue, we just take the results from those checkers.
If you think that one of the reported issues should not be an issue, the best place to discuss this is on the communities for each checker. It can help them fix bugs if needed, or to fine tune some rules.
How to provide feedback
W3C Markup Validator
You can provide feedback to the W3C Markup Validator team here:
Axe A11Y engine
You can provide feedback to the Deque Axe team here: