Heading outliner. H1 to H6. Warnings in context.
Paste HTML or page source. Get a visual outline of every H1 through H6 with warnings for missing H1, skipped levels, duplicate H1s, and empty headings. SEO and accessibility both depend on this hierarchy.
Source or snippet.
Headings are the spine.
Every well-structured page is a nested outline. One H1 names the page; H2s name major sections; H3s name sub-sections; H4-H6 handle deeper nesting when needed. Screen readers treat this outline as the primary navigation structure, and search engines infer topic hierarchy from it. When levels skip (H1 to H3, no H2) or duplicate (two H1s), both audiences lose the thread. The outliner above flags every problem with the specific position in the document.
Four heading rules. One, exactly one H1 per page naming the primary topic. Two, no skipped levels (H2 always before H3, H3 always before H4). Three, no empty headings (content only, no decorative tags). Four, avoid relying on visual CSS to communicate hierarchy; use the semantic tag that matches the content's level in the outline. All four are WCAG 1.3.1 requirements.
Tools in the same cluster: Website Audit for the full Lighthouse SEO and accessibility score. Color Contrast Checker for WCAG color compliance. Meta Tag Generator for the head-tag layer.
Five answers.
Why does heading hierarchy matter?
Two reasons. One, screen readers use heading levels to build a page outline users navigate with keyboard shortcuts; skipping from H1 to H3 with no H2 breaks that navigation. Two, search engines use heading hierarchy to infer page structure and relative importance of content blocks; a correctly nested outline correlates with better ranking and richer featured-snippet eligibility. WCAG 2.1 Success Criterion 1.3.1 requires programmatically determinable structure, which heading nesting is the main way to provide.
Should I have only one H1 per page?
One H1 per page is the traditional recommendation and the safest default. HTML5 introduced sectioning elements (section, article) that in theory allow nested H1 tags per section, but browsers and screen readers have never fully adopted that model. Google has stated multiple H1s do not hurt rankings but single H1 remains the convention for clarity. The outliner flags pages with zero or more than one H1.
What counts as a skipped heading level?
Going from H1 directly to H3 without an H2 between them skips a level. Going from H2 to H4 also skips. Screen readers interpret this as a broken outline. Occasionally designers jump levels for visual weight; the fix is CSS, not markup. Style an H3 to look like an H2 if needed, but keep the semantic hierarchy correct. The outliner flags every skip with the specific levels involved.
Does this tool fetch URLs?
No. Paste HTML source directly. Same-origin browser security (CORS) blocks client-side tools from fetching arbitrary URLs, and routing fetches through a Digital Heroes server would defeat the zero-server-state privacy promise. View page source in your browser, copy the relevant markup, and paste it in.
Does this tool save my data?
No. Every value you enter lives in memory for this browser tab only. Nothing is transmitted to a server, stored in a database, or synced. Close the tab and the data is gone.
Broken outline across templates?
Our SEO engagements audit every template (home, product, blog, collection, landing) for heading hierarchy plus content-SEO hygiene and ship correct semantic markup end-to-end.