Paste the HTML source of several pages at once — separated by a page-break line — and check H1-H6 hierarchy for every page in one pass: missing H1s, skipped levels, duplicate H1s, and empty headings.
Paste full page HTML (view-source, not the rendered page). Separate multiple pages with a line containing just -----. Optionally start a page's block with ### Page name to label it in the results.
Missing H1 — every page should have exactly one, describing what the page is about. Without one, search engines and screen readers both lose the clearest signal of the page's primary topic. Multiple H1s — technically valid HTML5, but it dilutes which heading is "the" title of the page, and most SEO guidance (including Google's own John Mueller) still recommends sticking to one. Skipped levels — jumping from H2 straight to H4 without an H3 in between breaks the logical outline that screen reader users rely on to navigate by heading, and gives search engines a less coherent structure to parse. Going back up a level (H3 to H2, to start a new section) is normal and not flagged. Empty headings — a heading tag with no text content serves no purpose and creates a confusing blank landmark for assistive technology.
Heading structure problems are rarely isolated to a single page — a CMS template, a component library, or a copy-paste habit tends to repeat the same mistake across every page that uses it. Checking pages one at a time makes it easy to miss that a "missing H1" issue is actually a template-wide problem affecting fifty pages, not a one-off. Pasting a batch at once surfaces that pattern immediately.
Right-click the page and choose "View Page Source" (or press Ctrl+U / Cmd+Option+U), select all, and copy — this gives you the actual HTML sent by the server, not the possibly-modified DOM after JavaScript runs. For pages where headings are inserted client-side by JavaScript, use your browser's Elements/Inspector panel instead and copy the rendered HTML from there, since view-source won't show anything JavaScript added after the initial load.
It's not invalid HTML5, and Google has said its crawlers can handle multiple H1s without penalty. That said, most practical SEO guidance still recommends one H1 per page, since it keeps the "what is this page about" signal unambiguous for both search engines and human readers scanning the outline — treat multiple H1s as a code smell worth reviewing, not an automatic ranking penalty.
No — moving back up to a higher (numerically lower) heading level to start a new section is normal and expected in any multi-section page. Only a downward jump of more than one level (H2 straight to H4, skipping H3) gets flagged.
Not currently — this tool works entirely in your browser with no server-side fetching, so it can only analyze HTML you paste in yourself. This also means nothing about the pages you check is ever sent anywhere.