Paste your full HTML page or just the body content
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Paste HTML and click Check Structure// validate heading hierarchy for accessibility & seo
Check your HTML heading hierarchy instantly. Detect missing H1, skipped levels, and accessibility issues in your page structure. Free, browser-based.
Ready to analyze
Paste HTML and click Check StructureCopy your full page HTML or just the heading tags into the input box.
Press Check Structure to analyze heading hierarchy instantly.
Review the visual outline and issue list, then correct your markup.
Heading Structure Checker analyzes HTML heading tags (H1–H6) to validate your document outline. A correct heading hierarchy is essential for screen reader accessibility and helps search engines understand page structure.
The H1 represents the main topic of a page. Multiple H1s confuse both search engines and screen readers about what the page is primarily about. SEO best practice and WCAG guidelines recommend exactly one H1 per document.
A skipped level occurs when you go from H2 directly to H4, for example, without using H3 in between. This breaks the logical document outline and can confuse assistive technologies that navigate by headings.
Yes. Search engines use heading hierarchy to understand content structure and importance. A clear H1 → H2 → H3 outline helps crawlers determine the main topic and subtopics of your page, which can influence rankings.
Yes — you can paste a full HTML document, just the <body> content, or even a plain list of heading tags. The checker will extract and analyze whatever heading elements it finds in your input.
This tool checks against WCAG 2.1 success criterion 1.3.1 (Info and Relationships) and 2.4.6 (Headings and Labels), detecting missing H1, duplicate H1, skipped levels, and empty heading tags.
The analysis is processed server-side using PHP's DOMDocument parser, but your HTML is never stored or logged. Each request is stateless and your content is discarded immediately after analysis.
A Heading Structure Checker is a development and accessibility tool that analyzes the HTML heading tags within a webpage — H1 through H6 — to ensure they follow a logical, hierarchical order. The heading outline of a document is fundamental to both web accessibility and search engine optimization, and errors in heading structure are among the most common HTML mistakes found in production websites.
Screen reader users rely heavily on headings to navigate web pages. According to WebAIM's annual survey, navigating by headings is one of the most common ways visually impaired users explore a page. When headings are missing, duplicated, or jump illogically from H2 to H4, screen reader users lose the ability to understand the page structure and jump to relevant sections efficiently.
WCAG 2.1 Success Criterion 1.3.1 (Info and Relationships) requires that information conveyed through visual presentation — such as section hierarchy — be available to assistive technologies. Proper heading markup is the primary way to satisfy this requirement for page structure. Success Criterion 2.4.6 further requires that headings and labels describe their topic or purpose when present.
Search engines like Google use heading tags as strong signals for understanding page content. The H1 tag is particularly important — it should clearly state the primary topic of the page and typically aligns with or matches the page's title tag. Subheadings (H2, H3) help search engines identify subtopics and understand content hierarchy, which can influence featured snippet eligibility and topical authority.
A well-structured heading outline also improves click-through rates: pages with clear, logical headings tend to have lower bounce rates because users can quickly determine whether the page addresses their query.
Think of your page's heading structure like a nested table of contents. The H1 is the book title, H2 tags are chapters, H3 tags are sections within chapters, and so on. A well-formed outline looks like:
Any deviation from this logical nesting — such as an H4 appearing before any H3, or an H1 appearing mid-page — constitutes a structural error that this tool will flag.
Paste any HTML content into the input area — it can be a complete HTML document, just the body content, or even a snippet with only heading tags. The checker will extract all heading elements in document order, build a visual outline tree, identify any hierarchy violations, and report specific issues with actionable descriptions.
For each issue found, the tool reports the type of problem (skipped level, missing H1, empty tag, etc.) along with the specific heading index where the problem occurs, making it easy to locate and fix the issue in your source code.