Disclosure: this post is written by the team behind KDP Quick Scout. This isn’t legal advice, publishing policies change, always check KDP’s own current guidelines before you rely on anything here.
Every KDP title gets seven backend keyword fields, each capped around 50 characters, hidden from readers and rarely touched after the first five minutes of publishing. Most authors either leave them half-empty or fill all seven with the first thing that comes to mind. Neither is really a mistake so much as a missed field, seven free shots at showing up in search that most books never use.
What backend keywords do
Amazon indexes these fields by individual word, not by the phrase as a whole. If your seven slots are “cozy mystery,” “small town mystery,” “amateur sleuth mystery,” and four more variations all built around the word “mystery,” you’ve spent seven fields’ worth of space repeating one word six times over. The words that add reach are the ones you haven’t used yet.
That’s also why generic single words are close to wasted space. Amazon’s own guidance on this is direct: avoid vague keywords, and use specific ones instead of general ones. A book titled “America’s National Parks” gains more from “Yellowstone” and “Grand Teton” than from “parks,” because “parks” is already implied by the title and the category.
What KDP’s own rules say
Straight from Amazon’s KDP help pages, not a secondhand summary:
- No subjective quality claims. “Best novel ever,” “must read,” anything that’s an opinion rather than a description.
- No time-sensitive language. “New,” “on sale,” “available now,” anything that goes stale.
- No Amazon program names. “Kindle Unlimited” and “KDP Select” are explicitly called out as off-limits in keyword fields.
- No other authors’ names, unless they’re genuinely associated with your book (a co-author, a series you’re actually part of).
- No promotional or rank claims. “Bestselling,” “free,” “#1” and similar.
- Think like a search query, not a label. Amazon’s phrasing: imagine how you’d search if you were a customer. “Military science fiction,” not “fiction science military,” since that’s not how anyone types.
None of this is exotic. It’s mostly common sense once you see it written out, which is exactly why it’s easy to skip reading and just guess instead.
A worked example
Say you’re publishing a cozy mystery: amateur baker solves murders in a small coastal town, first in a planned series. A first-pass, guessing approach might produce something like: “mystery,” “cozy mystery,” “murder mystery,” “detective,” “crime,” “suspense,” “thriller.” Every one of those either repeats a word already used elsewhere in the set, or is too broad to mean much on its own (“crime” and “suspense” describe half the mystery section).
A word-diverse pass looks more like: “small town murder mystery,” “amateur sleuth bakery,” “cozy mystery series,” “female detective coastal town,” “culinary cozy mystery,” “book club mystery pick,” “quirky small town characters.” Same genre, same book, but seven fields now cover baking, coastal setting, amateur-detective tropes, series intent, and even a book-club-audience angle, instead of six ways of saying “mystery.”
The part nobody does: revisiting them
KDP’s own guidance is explicit that keywords aren’t a one-time setting: you can and should update them as you learn what’s driving traffic. Almost nobody does this. The five minutes spent at first publish become the permanent keyword set for a book’s entire life, even after months of sales data exist that would tell you which genre angles are converting.
Where this gets easier
Filling seven fields well means avoiding word overlap by eye across seven boxes at once, which is more bookkeeping than it sounds like for a two-minute task most authors want to finish quickly. KDP Quick Scout’s Keywords tab pulls real related-search phrases from Amazon’s own autocomplete for whatever phrase you’re considering, then auto-fills up to seven backend-keyword slots that avoid repeating a word across fields, already filtered against the promotional-language rules above. It doesn’t know your book better than you do, so the suggestions are a starting point to edit, not a final answer, but it removes the “did I just say mystery six times” problem before you publish.