What it checks
- One H1
- One main heading that says what the page is about. None, or several, makes the topic harder to read.
- Heading order
- Going from H2 straight to H4 skips a level. Screen readers and crawlers use the levels as the page's outline.
- Empty headings
- A heading with no text (often an icon or a styling hook) adds noise to the outline.
It reads the HTML your server sends, before JavaScript runs. Headings added later by scripts don't show here, and some crawlers miss them too.
