Clean HTML without critical errors
Your HTML should parse cleanly without unclosed tags, duplicate IDs, or structural errors.
Why HTML hygiene matters
Modern browsers are forgiving — they fix broken HTML on the fly. AI crawlers are less forgiving. They use simpler parsers that can choke on unclosed tags, mismatched elements, or duplicate IDs. When the parser chokes, it either skips content or misinterprets structure.
The most expensive failure is not a total parse error; it is subtle structural confusion that makes the crawler think one section is nested inside another. Your navigation becomes part of your article. Your footer becomes part of your main content.
Common critical errors
- — Unclosed div or section tags.
- — Duplicate id attributes.
- — Mismatched nesting (p inside p, ul inside a).
- — Missing required attributes on form elements.
- — Mixed content (http images on an https page).
How to check
Run the W3C HTML validator against your homepage and any pages where structure matters. Fix everything it flags as Error. Warnings are usually safe to ignore.