Pick an Amazon KDP category and see how hard it is to break into — scored from real Best Sellers data, with the numbers behind the score shown in full. No sign-up, no card.
The score blends three parts. Demand is weighted highest at 60%, competition at 25%, and monetisability at 15%. Where a part has no data behind it, the remaining weights are renormalised rather than the missing part being silently scored as zero — so a category never looks worse simply because one signal hasn't been collected yet.
The competition component uses the median review count of the ranked titles in the category. That number is the entry bar: it tells you how much accumulated reviewing history a new book has to compete against. A median in the hundreds is a category you can realistically enter; a median in the thousands means the top of that list has been building for years. Median is used rather than average because one runaway bestseller with 40,000 reviews would drag an average somewhere no real book in the category actually sits.
It does not report sales, revenue, or royalties for any book or category. Amazon does not publish those figures, so nothing here estimates them. Every number shown is either read directly from Amazon's public Best Sellers pages or is a stated transformation of those numbers, and the basis line under each score names the real values it used and when they were collected.
If a category returns no score yet, that means the data collection for it hasn't run — not that the category is empty. The tool says so plainly instead of showing a zero.
A high score means demand looks strong relative to how crowded the category is. It is a shortlisting signal, not a verdict. Your cover, interior quality, keywords, and pricing still decide whether a specific book sells.
Amazon Best Sellers data is collected daily. Each result shows the collection date in the basis line, so you can see for yourself how current it is.
Review count is the one competitive signal Amazon publishes openly on Best Sellers pages. It is a proxy for how established the incumbents are, not a sales figure, and it is labelled that way everywhere it appears.
Picked a category? These take you the rest of the way to a print-ready book.
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