Clearscope and Surfer charge $99-$399/month to tell you which subtopics your competitors cover and you don't. The measurement they run is public — extract H2 and H3 headings from the top-ranking pages, cluster by topic similarity, show what's missing.
The Heading Gap Audit runs the same measurement for free. Paste your article URL plus 2-5 competitor URLs. Output: topical coverage %, missing-topic list, unique-to-you list, and an AI outline-fix prompt.
How matching works
H2 and H3 headings from all pages are clustered by token-overlap similarity (Jaccard ≥ 0.5). Each cluster represents one subtopic. For each cluster, the tool checks whether any of your headings match it (Jaccard ≥ 0.45 — slightly lower threshold because cross-competitor matching is stricter than mine-vs-theirs).
A topic covered by 3 of 5 competitors but not you is a strong candidate to add. A topic covered by 1 of 5 is niche — may be tangent not worth adding. A topic only you cover is differentiation — but it could also be an unfocused tangent; review before keeping.
What the output looks like
Three sections:
- Competitor topic clusters with coverage indicator. Every subtopic from competitor pages, sorted by competitor-count descending. Green border = you cover it. Red border = you don't.
- Unique-to-you topics. Your H2/H3s that don't match any competitor cluster. Review whether genuine differentiation or just tangent.
- AI outline-fix prompt. Paste into Claude / ChatGPT → get new H2 sections + one-paragraph bodies for the missing topics, grouped into a publishable revision.
Why H2/H3 and not content depth
Headings are a strong proxy for what the page covers without needing to parse full content. Two articles with similar H2 structure usually cover similar topics in the same depth. A paid tool's "content score" is a more sophisticated signal, but the heading-gap signal catches 70-80% of real gaps.
For content-depth analysis beyond headings, follow up with Passage Retrievability on each new section as you write it, and AI Citation Readiness on the finished article.
Related reading
- Headings Outline — single-URL H1-H6 outline + errors
- FAQ Harvester — pulls FAQPage content from top-10 SERP
- Keyword Inspection — SERP top-10 analysis
Fact-check notes and sources
- Clearscope methodology (content score): clearscope.io/about
- Surfer content editor: surferseo.com
- Jaccard index: en.wikipedia.org/wiki/Jaccard_index
The $20 Dollar Agency covers content-gap audits as a recurring client deliverable. The tool is the measurement half; the book is the pricing and packaging half.
