The best keyword clustering tools, and how they differ

Tools differ mainly in the signal they use.

Dedicated SERP-based clustering tools include Keyword Insights, KeywordCupid, and Cluster AI. All-in-one suites offer clustering inside their keyword tools: SE Ranking has a keyword grouper, Semrush groups keywords in its Keyword Strategy Builder, and Ahrefs assigns a parent topic to each keyword. Several free tools cluster small lists semantically or by SERP for a limited number of keywords. Most charge per keyword or by credits for SERP-based work.

SERP-based tools ask how many shared URLs make two keywords one cluster. A lower threshold creates bigger clusters and fewer pages; a higher one creates more, narrower pages. Three or four shared URLs in the top ten is a common starting point. When planning this site, we treated two keywords as one intent when their top ten shared four or more URLs, and merged several planned pages as a result.

Pick ten clusters at random. For each, search the primary keyword and one secondary keyword and compare the first page of results. If the same pages rank for both, the cluster is sound. If the results are different types, for example tools for one and guides for the other, split the cluster. Also check that no cluster duplicates a page you already have; that is an optimisation task, not a new page.

Each cluster becomes one page with one primary keyword, the secondary keywords covered naturally in headings and sections, and a format that matches the results Google shows. Our guide to keyword cannibalisation explains how to fix existing pages that overlap. SerionFlow is the wrong tool for a one-off clustering job; a dedicated clustering tool is the cheaper option for a few hundred keywords.