Before a search engine or a screen reader reads a single word of body text, it reads the heading tags — H1 through H6 — as a nested outline of what the page covers and how the parts relate. Get that outline right and both readers understand the page in one pass; get it wrong (no H1, headings that skip levels, the outline that doesn’t match how the content actually nests) and the structure has to be inferred instead of read.

The three things this checker looks for

• Exactly one H1. It’s the single clearest signal of what the page is about — the same job a chapter title does in a book. Zero H1s leaves nothing playing that role; more than one splits it between two claims about what the page covers.
• No skipped levels.An H2 followed directly by an H4, with no H3 in between, breaks the nesting a screen reader announces (“entering a sub-section” two levels deep with nothing marking the level in between) and the outline a search engine builds from the hierarchy.
• No duplicate heading text.Usually harmless — a long guide can legitimately repeat “Summary” in more than one section — but worth a glance when it’s the entire outline repeating, which usually means a template rendered the same block twice.

What headings are not for

A heading tag exists to mark structure, not to make text bigger or bold. A line wrapped in <h3> purely because the design wanted larger text there — with no actual sub-section starting — reports a false structure to anything reading the outline. If the goal is visual size, that’s what CSS font-size is for; the heading tag should track what the content is actually structured as.

How this differs from the SEO Optimization Checker

The SEO Optimization Checker includes a heading check as one of many signals across the whole page (title, meta description, links, structured data). This tool does one thing — the full outline, every heading in order, with the specific hierarchy problems named — for when the heading structure itself is what needs a closer look.

Frequently asked

Does heading structure directly affect rankings?

Google has said heading tags are one of many signals it uses to understand a page’s structure and topic, not a direct ranking factor on their own. The more concrete benefit is accessibility (screen readers navigate by heading level) and clarity for anyone skimming the page.

Can a page have more than one H1?

HTML5 technically permits it, especially inside separate <section> or <article> elements. Most SEO guidance still recommends exactly one per page as the safer, clearer default, which is the standard this checker applies.

Once I have the outline, how do I turn it into a linked table of contents?

See the Table of Contents Generator — it takes the same kind of heading outline and builds anchor-linked HTML or Markdown from it.