Heading hierarchy

Long definition

Heading hierarchy is the most basic document-structure signal you control. Crawlers parse <h1> through <h6> to build a topic outline: H1 names the page, H2s carve it into sections, H3s subdivide those sections, and so on down. Skipping levels (H2 → H4) or using multiple H1s breaks that outline.

The HTML5 spec once defined an "outline algorithm" that would auto-promote headings inside <section> and <article> elements, allowing multiple H1s without ambiguity. No browser ever implemented it, and the WHATWG HTML spec now explicitly recommends against relying on it. The practical rule is the pre-HTML5 one: one H1 per page, then H2/H3 nesting by topic.

For SEO, the H1 is the strongest on-page topic signal after the <title> tag. Google has confirmed it reads H1s and uses them in passage indexing — the system that surfaces a specific section of a long page for a query. Well-structured H2s give Google explicit handles to lift as featured snippets and "things to know" panels.

Accessibility runs on the same hierarchy. Screen readers (NVDA, JAWS, VoiceOver) let users navigate by heading level — broken hierarchy makes the page unusable for keyboard-and-screen-reader users. Roughly 7-8% of traffic on consumer sites uses assistive tech in some form.

LLM scrapers (GPTBot, ClaudeBot, PerplexityBot) parse the same structure to chunk content for retrieval. A page with clear H2/H3 sections gets clean chunks; a wall of <div> content gets chunked arbitrarily and quoted less precisely.

Common misconceptions

• "Multiple H1s are fine in HTML5." Technically valid HTML, but the outline algorithm that justified them was never shipped. Google has said it will tolerate multiple H1s but parses pages more cleanly with one.
• "H1 must contain the exact target keyword." It must describe the page accurately. Modern ranking handles synonyms and intent — a natural H1 like "How to register a sole proprietorship in Spain" beats a stuffed "Sole Proprietorship Registration Spain Sole Proprietor Guide".
• "Skipping H3 to H5 is invisible to crawlers." Crawlers tolerate it; screen readers don't. WCAG 1.3.1 (Info and Relationships) treats skipped levels as a structural failure.
• "Headings are styling tags." They're structural tags styled by CSS. If you want big bold text without a heading meaning, use a <p> with a class — don't use an <h2> for visual weight.