I’ve included some screenshots at the bottom of this post to show the full code I used to check under each doctype.

HTML Tidy is another option for validating pages, though it may not offer the exact same results as the W3C validator.

We've been using it (formerly Site Validator) since 2015 to validate the ecommerce sites we develop, I've no idea how we managed without it!

We've only been using Rocket Validator a short while but it's been incredibly powerful in helping us validate multiple large sites in a very short amount of time.

Web studios and freelance developers from all around the world use Rocket Validator to validate accessibility and HTML conformance on their sites as part of their web development process.

Our service helps them quickly identify the parts of their sites that need more attention, so they can be fixed and re-checked until they're valid.