The best keyword research tool is Amazon's own search bar, free and built into the site you're trying to rank on: type a candidate phrase, look at what comes back, and ask honestly whether those results look like your book. If they don't, that phrase is working against you, no matter how relevant it seems in your head.
This is part of the Complete Guide to Amazon KDP Keywords and Categories.
Type the start of a search phrase related to your book into Amazon's search bar and see what autocomplete suggests. These suggestions reflect real searches other shoppers have made, which makes them a genuinely useful signal of actual reader language, not guessed terminology. Try broad genre terms first, then narrow into more specific combinations (setting, character type, trope, tone) to see what autocomplete surfaces at each level.
Once you have a list of candidate phrases, search each one directly and study what comes back. Ask whether the results genuinely resemble your book; if a phrase returns titles that share little with yours in genre, tone, or content, it isn't a good match, even if it seemed thematically related on paper. Notice how many results come back, too: an enormous number means heavy competition, while a very small number might mean low reader search volume, and the sweet spot is usually a phrase specific enough to have manageable competition but common enough that readers are actually typing it. Finally, look at what ranks at the top for that phrase, how those books are positioned, their titles, covers, and review counts, since that tells you what you'd actually be up against.
Amazon's own keyword guidance points authors toward several categories worth brainstorming systematically, beyond just "genre": setting (where and when the story takes place), character type (who the protagonist or key characters are, like a single dad or a retired detective), character role (their function in the story, like a strong female lead or an unreliable narrator), plot themes (coming of age, redemption, forgiveness, revenge), and tone or mood (cozy, dark, feel-good, slow-burn, gritty). Readers increasingly search by mood and promise as much as by plot or genre. Terms like "clean read," "slow burn," "no cliffhanger," and "gripping page turner" are heavily searched in fiction and frequently overlooked by authors who focus only on plot description.
Search for books genuinely comparable to yours (not aspirational bestsellers, but titles with a realistic overlap in audience and scope) and study how they're positioned: their subtitle, description language, and which categories they're listed in. This isn't about copying their keywords directly, since your book isn't theirs, but it reveals the vocabulary and positioning that's already working in your specific niche.
Say a candidate keyword out loud and ask whether it sounds like something a real person would type, not like a description you'd write for yourself. "Post-apocalyptic survival series" and "first contact alien invasion thriller" both work because they're specific and sound like a genuine search; "science fiction" alone doesn't, both because it's too broad and because it's not how most specific searches actually get typed.
Once you've drafted your seven keyword fields, search each phrase one more time as a final check before publishing. This catches phrases that seemed right in isolation but don't actually return relevant results when tested directly.
Keyword research doesn't end at publication. Once your book has been live for a while, you'll have a better sense of which searches are actually converting versus which keywords generated views without sales. See How Often Should You Update Your Book's Keywords and Categories?
Need Help With Your Book's Metadata?
Entrada Publishing can help you think through keyword research as part of getting your book ready to publish.
Amazon's own search bar. Typing a candidate phrase and evaluating the results it returns is free, direct, and reflects the actual platform you're trying to rank on.
If a search for it returns an enormous number of results with no realistic connection to how a new or lesser-known book could rank, it's likely too broad. Narrowing to a more specific phrase usually improves your odds.
Not directly. Bestsellers already have massive review counts and visibility that a new keyword can't replicate for you. Study comparable titles closer to your own scope instead, for vocabulary and positioning, not to copy verbatim.
At least once before publishing, and again after your book has been live long enough to show you real search and sales data. See How Often Should You Update Your Book's Keywords and Categories?