The W3C graciously hosts the following free validation tools:
CSS Validator – Checks your Cascading Style Sheets (CSS)
Internationalization Checker – Checks level of internationalization-friendliness.
Link Checker – Checks your web pages for broken links.
Markup Validator – Checks the markup of your Web documents (HTML or XHTML).
RSS Feed Validator – Validator for syndicated feeds. (RSS and Atom feeds)
RDF Validator – Checks and visualizes RDF documents.
Unicorn – Unified validator. HTML, CSS, Links & Mobile.
Validator.nu Checks HTML5.
I mention that these tools are free to emphasize there is no barrier to their use.
Just as you wouldn’t submit a research paper with pizza grease stains on it, use these tools to proof draft standards before you submit them for review.