About

Search engines parse heading tags (h1 through h6) to build a semantic outline of your page. A broken hierarchy - where h1 jumps directly to h3, or multiple h1 tags compete for primacy - signals poor document structure to crawlers. Google's John Mueller has confirmed that heading order matters for accessibility and helps machines understand content relationships. Screen readers rely on heading levels to generate navigable outlines; a skipped level forces users to guess whether content is missing or misclassified.

This tool parses raw HTML or fetches a live URL, extracts every heading element, and validates the sequence against the W3C outline algorithm. It flags 6 distinct issue types: missing h1, multiple h1 tags, skipped levels, empty headings, excessively deep nesting beyond h4, and duplicate text across same-level headings. Results render as a visual tree so you can spot structural breaks at a glance. The checker operates entirely client-side. No HTML is transmitted to any server. Note: this tool analyzes the raw DOM output. If your page relies on JavaScript-rendered headings (SPA frameworks), paste the rendered HTML source rather than the template markup.

Formulas

The heading hierarchy is validated by tracking the current depth level d as headings are encountered sequentially. For each heading h_i with level l_i (where l ∈ {1, 2, 3, 4, 5, 6}), a skip error is flagged when:

l_i − l_i−1 > 1

This means the document jumps from level l_i−1 to l_i without an intermediate heading. Decreasing levels (e.g. h3 → h2) are always valid as they represent closing a subsection.

The SEO score S is computed as:

S = 100 − E_wN × 100

where E_w = weighted error count (critical = 3, high = 2, medium = 1), and N = total headings + 1. The score is clamped to [0, 100].

Reference Data

Issue Type	Description	SEO Impact	WCAG Violation	Fix Priority
Missing h1	No h1 tag found on page	High - crawlers lose primary topic signal	WCAG 1.3.1 (A)	Critical
Multiple h1	More than 1 h1 tag present	Medium - dilutes topic focus	Best Practice	High
Skipped Level	Heading level jumps (e.g. h2 → h4)	Medium - breaks content outline	WCAG 1.3.1 (A)	High
Empty Heading	Heading tag contains no text content	Low - wasted crawl signal	WCAG 1.3.1 (A)	Medium
Deep Nesting	Usage of h5 or h6 tags	Low - rarely indexed deeply	None	Low
Duplicate Text	Same text in multiple headings at same level	Low - redundant signals	None	Low
Very Long Heading	Heading exceeds 70 characters	Low - may be truncated in SERPs	None	Low
First Heading Not h1	Page starts with h2 or lower	Medium - unclear primary topic	Best Practice	High
Non-Sequential Decrease	Heading goes from h3 back to h1	Low - valid but unusual	None	Info
Heading Inside a	Heading wrapped in anchor tag	Low - link weight transfer	None	Info
Recommended h1 Length	20 - 70 characters optimal	Medium - affects CTR in SERPs	None	Medium
Max Recommended Depth	Most pages need only h1 - h4	Low - h5/h6 rarely useful	None	Info
Ideal Heading Count	5 - 15 headings per 1000 words	Medium - content scannability	None	Medium
Keyword in h1	Primary keyword should appear in h1	High - strongest on-page signal	None	High
Heading Ratio	Headings should be < 20% of body text	Low - thin content flag	None	Info

Frequently Asked Questions

The HTML5 specification technically allows multiple H1 tags when using sectioning elements (<article>, <section>). However, Google recommends using a single H1 per page for clarity. Multiple H1 tags dilute your primary topic signal and confuse screen reader navigation. This tool flags any page with more than one H1 as a high-priority issue.

Skipping levels (e.g., jumping from H2 to H4) does not directly trigger a ranking penalty. However, it violates WCAG 1.3.1 accessibility guidelines and signals poor document structure to crawlers. Screen readers generate a heading outline for navigation; skipped levels create gaps that confuse visually impaired users. Search engines use heading hierarchy to understand content relationships, so a clean structure indirectly supports better content interpretation.

Most well-structured content requires only H1 through H4. Usage of H5 and H6 typically indicates either over-segmentation of content or misuse of heading tags for styling purposes. If you genuinely have 5+ levels of nested topics, the warning is informational. But in practice, content nested that deeply is often better restructured into separate pages or sections.

Yes. Enter a URL and the tool fetches the page HTML via a CORS proxy. Note that pages relying on client-side JavaScript rendering (React, Vue, Angular SPAs) may return incomplete HTML since the proxy fetches raw server response without executing JS. For SPAs, open the page in your browser, right-click "View Page Source" or use DevTools to copy the rendered DOM, then paste it into the HTML input tab.

Google displays roughly 50-60 characters of a title tag in SERPs, but H1 tags are not truncated in search results directly. For readability and SEO, keep H1 between 20 and 70 characters. An H1 shorter than 20 characters may lack descriptive keywords. An H1 longer than 70 characters becomes difficult to scan and may indicate keyword stuffing. This tool flags headings outside this range.

No. All HTML parsing and analysis happens entirely in your browser using the native DOMParser API. When you paste HTML, it never leaves your machine. The only network request occurs when you use the URL fetch feature, which routes through a public CORS proxy (api.allorigins.win) to retrieve the page HTML. The proxy sees the URL but not your analysis results.