9 Best Keyword Clustering Tools in 2026

Methods, limits and prices below come from each vendor's own feature, help and pricing pages, checked on 12 October 2026, and are 'as of October 2026'. Where a vendor's pages disagree with each other, we say so.

Two ways to cluster

SERP-overlap clustering searches each keyword, records the top results, and groups keywords whose result pages share a set number of URLs. It reflects how Google treats the keywords today, which is what matters for deciding one page or two, but every keyword costs a search. Semantic clustering groups keywords by meaning using language models. It is fast and cheap and works without search data, but it can merge keywords Google treats as different intents. Most tools here use SERP overlap; Surfer's Topical Map, Zenbrief and SEO.ai's free tool are semantic.

At a glance (as of October 2026)

The tools, one by one

Keyword Insights: clustering plus briefs

Keyword Insights clusters by comparing the top search results: its documentation says keywords sharing 40% or more of their URLs form a cluster, while its feature page gives a 30% default, so check the setting. You can choose between two algorithms and up to 200,000 keywords per job. Clustering costs 1 credit a keyword, a brief 100 credits and a writing-assistant article 200. Basic is $58 a month with 10,000 credits and Professional $99 with 20,000 (annual billing saves 20%), and a 7-day trial costs $1. Clustering supports about 130 languages, while briefs and writing support about 20. Best for: agencies that go from keyword list to brief in one tool. Limit: credits are shared with briefs and writing.

KeyClusters: pay only for what you cluster

KeyClusters groups keywords that share 3 or more of the same top-10 ranking pages, for any geography and desktop or mobile. There is no subscription: 2,500 keywords cost $19, 20,000 cost $110 and 100,000 cost $350, which works out at $7.60 down to $3.50 per 1,000, and credits never expire. It imports Ahrefs and Semrush exports and exports to CSV or Excel. Best for: occasional large clustering jobs. Limit: clustering only, with no briefs or writing.

Thruuu: clustering, briefs and AI answer checks

Thruuu clusters by URL overlap with an adjustable threshold (4 to 10 shared results in the top 10). Clustering 1,000 keywords costs 50 credits and a content brief 5 credits. Monthly plans are $19, $49 and $99 (Starter, Pro, Agency) with 75, 250 and 700 credits and batches of 5,000, 10,000 and 15,000 keywords; annual plans are $13, $33 and $66 a month, paid upfront. A free tier gives 10 one-time credits for US English. Paid plans cover 196 countries and 151 languages, and higher plans add AI Overviews and LLM answer analysis. Best for: small agencies that want clustering and briefs cheaply. Limit: credits are shared between clustering and briefs.

Serpstat: clustering inside a budget suite

Serpstat groups keywords by URLs that appear together in the top 30 results, with weak (3 shared URLs), medium (8) and strong (12) settings and soft or hard cluster types. Each keyword costs 5 credits, changing the settings is free, and a project holds 3 to 50,000 keywords. It is available from the Individual plan ($69 a month, $50 billed annually), whose 5,000 tool credits cover about 1,000 keywords a month and are shared with text and batch analysis. Best for: Serpstat users. Limit: 5 credits a keyword is expensive at volume.

SE Ranking Keyword Grouper

SE Ranking's grouper matches keywords by shared ranking URLs; you set the minimum number of matching URLs and the clustering method. Its page says adding a search volume check increases the price by $0.005 per query; the help article with the base rate did not load for us. SE Ranking plans start at $129 a month with a 14-day trial without a card. Best for: SE Ranking customers. Limit: confirm the per-query rate before running a large job.

Semrush Keyword Strategy Builder

Semrush compares the top 10 organic results for each keyword and groups keywords that return similar URLs into clusters, then maps them into a content plan. Its knowledge base says all subscriptions can store up to 200,000 keywords across lists and import 2,000 at a time, while a Semrush blog post gives lower totals, and the knowledge base still uses older plan names for monthly clustering limits. Plans start at $139 a month. Best for: Semrush customers planning content. Limit: check the current limits in your account.

Ahrefs Keywords Explorer

Ahrefs offers two groupings: clusters by parent topic, which uses the keyword that sends the most traffic to the top-ranking page, and clusters by terms, which groups keywords by shared words rather than intent. Ahrefs' pricing page lists keyword clusters from the Standard plan ($249 a month). No trial. Best for: Ahrefs Standard users. Limit: term clusters are lexical, so check intent yourself.

Surfer Topical Map

Surfer's Topical Map finds neighbouring topic clusters by semantic similarity, using your site's Google Search Console data. It is on the Pro ($182 a month billed yearly) and Peace of Mind plans, refreshes every 14 days, and smaller or newer domains may not qualify. 7-day free trial of Pro. Best for: planning content around what your site already ranks for. Limit: needs a connected, established site.

Zenbrief: semantic clustering

Zenbrief's clustering tool uses transformer embeddings plus clustering and graph algorithms rather than search results. The free tier handles 5,000 keywords per session in English; a paid tier handles up to 100,000 keywords a month, at a price its page does not state. Its brief plans start at $195 a month for 30 briefs. It supports English, French, German, Italian and Spanish. Best for: fast first-pass grouping of very large lists. Limit: semantic groups need a SERP check before you commit a page to them.

Others worth knowing

ClusterAi (contentdistribution.com) clusters up to 25,000 keywords by SERP overlap with a free start and no card; WriterZen sells one-time licences from $135 that include clustering of up to 10,000 or 20,000 keywords.

What 10,000 keywords cost to cluster

Clusters and AI answers

Clustering decides how many pages you need; it does not tell you whether an assistant will quote them. A cluster is also a good unit for checking AI answers: write the cluster's main question as a prompt and ask ChatGPT, Gemini, Perplexity and others whether your client is named. Fenn runs those checks across ChatGPT, Claude, Gemini, Perplexity and Grok when you start them, and drafts answer-first pages of 500 to 800 words for the gaps, flagging the facts only the client can supply. It does not cluster keywords. Plans start at $29 a month, set up after a demo.

FAQ

What is the cheapest keyword clustering tool?

As of October 2026, KeyClusters at $3.50 to $7.60 per 1,000 keywords (pay as you go, no expiry) and Thruuu's annual plans are the cheapest per keyword. Zenbrief's free tier clusters 5,000 English keywords per session semantically.

Is SERP-based clustering better than semantic clustering?

For deciding whether keywords share a page, SERP overlap is closer to how Google treats them today. Semantic clustering is faster and cheaper for a first pass on very large lists.

Does Semrush have keyword clustering?

Yes. Keyword Strategy Builder groups keywords whose top-10 results share URLs and maps them into a content plan. Check the current list and clustering limits in your account, as Semrush's own pages give different figures.

How many shared URLs make a cluster?

It is a setting. KeyClusters uses 3 shared top-10 pages, Serpstat offers 3, 8 or 12 shared URLs in the top 30, Thruuu lets you choose 4 to 10, and Keyword Insights uses a percentage overlap.