Heading Structure Validator
Your HTML is parsed for analysis only: it is never rendered, and nothing leaves your device.
How it works
仕組みPaste your page’s HTML and see its heading skeleton the way a screen reader hears it: an indented outline of every H1-H6 in document order. The validator flags a missing H1, more than one H1, skipped levels like jumping from H2 straight to H4, and headings with no text at all. Screen-reader users routinely navigate by jumping between headings, so a clean hierarchy is one of the cheapest accessibility wins there is, and search engines lean on the same structure to understand your page. Analysis only; your markup is never rendered.
HTML5 technically allows it, and it won’t break anything outright. But most accessibility guidance, and plenty of screen-reader users, expect a single H1 that names the page, like a book’s title. Multiple H1s make the outline ambiguous, so this tool marks extras as a warning rather than a hard error.
Don’t: heading tags describe structure, not size. If H3 looks too big in your design, keep the H3 tag and restyle it with CSS. Skipped levels sound like missing sections to someone navigating by headings, and automated audits like Lighthouse and axe flag them too.
Yes, completely. Moving back up the ladder just means the current subsection ended and a new major section is starting, exactly like chapters and subchapters in a book. Only downward jumps that skip a level (H2 to H4) are a problem, and this validator only flags those.