Amazon backend keywords: the search terms rules, and what to put in them

Every Amazon listing has a field that shoppers never see. Amazon calls it Search Terms in Seller Central and generic keywords in its templates, and sellers call it backend keywords. It exists for the words people search with that don’t belong on the page: the synonym your customers use, the abbreviation, the alternative name.

This guide covers that one field. It is part of our Amazon SEO series, which explains how Amazon search decides what to show. For choosing which terms to use in the first place, see our guide to Amazon keyword research; for the visible parts of the listing, see Amazon listing optimisation.

What backend search terms are for

Amazon’s UK help describes them simply. Sellers can add search terms that “should only include generic words that enhance the discoverability of your product”, and its example is headphones, where the search terms might include “earphones” and “earbuds”. They “are hidden from the customers"².

That makes the field useful for one job: covering the ways shoppers search for your product that the visible listing doesn’t already cover. It is not a second title, a place for competitors’ names or a dumping ground for every keyword a tool suggests. And since 27 July 2026 it matters a little more, because titles on Amazon.co.uk are limited to 75 characters⁵. Words that used to sit in a long title now need a new home, and the hidden field is one of three, alongside item highlights and bullets.

The current UK rules

These are Amazon’s rules for the Search Terms field on Amazon.co.uk, as its help pages stated them on 1 October 2026.

Amazon’s list of prohibited temporary words is longer than most sellers expect: “available now”, “brand new”, “current”, “discounted”, “just launched”, “last chance”, “latest”, “limited time” and “today” are all on it, as are subjective words such as “effective”, “fastest”, “popular” and “trending"¹.

Two pieces of older advice no longer hold. The field used to be five fields with up to 5,000 bytes; Amazon reduced it to one “to improve the quality of Amazon search results and reduce the amount of superfluous search terms"¹. And several other keyword attributes have faded: Amazon says intended use, other attributes and target audience are “primarily used in the U.S.” and being phased out, and that platinum keywords are now redundant³.

How bytes are counted

The limit is in bytes because some characters take more than one. Amazon’s help explains that alphanumeric characters (a to z, A to Z, 0 to 9) are one byte each, that a character such as the German ä “can be 2 bytes”, and that Japanese and Chinese characters can be 3 or 4¹. That follows from UTF-8, the standard encoding on the web, which uses one byte for basic Latin characters and two, three or four for everything else⁶.

For most English-language listings this makes no difference, because almost every character is one byte. It matters in three cases: products with accented names (crème brûlée dishes, jalapeño sauces, café furniture), any listing where someone has pasted in symbols, and anyone who fills the field right to the limit. “crème brûlée dish” is 17 characters but 20 bytes.

There is one ambiguity in Amazon’s own wording. It says spaces and punctuation are not counted when it calculates the length¹, but the same page says the Seller Central field has a counter that stops accepting input at the limit¹. In our practice we keep the whole field, spaces included, under 249 bytes. It costs a word or two at most, and the penalty for misjudging it is losing every term.

What happens if you go over the limit

Nothing visible. The listing stays live, the field may look fine in Seller Central, and Amazon doesn’t send a warning. But, in Amazon’s words, if search terms are over the limit, “none of the Search Terms for that ASIN will be indexed"¹. Not the excess: all of them.

That is different from how Amazon treats its other keyword attributes, where “Amazon Search indexes up until the length limit and ignores any excess"³. The Search Terms field is the exception, and the one that matters most. Be most careful with bulk uploads and with copies between marketplaces, where a German or French translation can carry multi-byte characters into a field that was close to the limit in English.

Worked examples

Both examples are illustrations, for products of the kind we work on.

Amazon’s rules don’t say whether to repeat words that are already in the title, only not to repeat words within the search terms field¹. In our practice we don’t repeat them: the title and item highlights are already indexed, and the bytes are better spent on new words. Amazon says item highlights are searchable¹⁰, so the same applies to them.

How to check your backend terms are indexed

Amazon doesn’t offer a report that lists which of your search terms are indexed. This is the routine we use instead.

For the second step, Amazon lists the five common reasons an ASIN is unsearchable, and its help includes a tool called “Determine why an ASIN is not searchable” that diagnoses a specific search URL⁴. For the last, Search Query Performance shows impressions, clicks, basket adds and purchases for searches associated with your brand, counting organic and Sponsored Products results from the search page⁸. Amazon says indexing makes an ASIN “eligible (but not guaranteed)” to appear for a search¹, so a term that is indexed but irrelevant may still bring nothing. That is a reason to choose terms well, not to add more.

Why it is worth the hour: free relevance

Backend search terms cost nothing to change and nothing per click. Every search you win organically is a search you don’t have to buy.

Say one synonym your listing didn’t cover brings 40 organic orders a month once it is in the field. Buying those 40 orders through Sponsored Products, at a 12% conversion rate and 60p a click, would take about 333 clicks and £200 of ad spend a month. At a margin of £5.00 an order, the same orders are worth £200 in profit before advertising, so paying for them would leave nothing. Earning them organically keeps all of it.

That is the logic we apply across a catalogue: get relevance for free where you can, through the title, item highlights, bullets and backend terms, and pay for clicks only where the margin covers them. Our PPC strategy guide covers the paid side, and our negative keywords guide covers how to stop paying for searches that don’t convert.

Common mistakes

1. Going over the limit, often through a bulk upload, a translation or pasted symbols. The cost is every term, not just the excess.
2. Brand names, your own or a competitor’s. They are prohibited, and the risk is suppression, not just wasted bytes.
3. Repeating the title, word for word. It is not against Amazon’s rules, but it spends bytes on words that are already indexed.
4. Misspellings and plurals. Amazon says neither is needed, and its research describes search that copes with spelling errors and word variants⁷.
5. Hiding facts shoppers need. If a buyer might ask about it, such as material, size or compatibility, it belongs on the visible page, where AI assistants and people can read it.
6. Setting it once and forgetting it. Revisit the field when your keyword research turns up new converting searches, and whenever you rewrite the title.

Then check the visible half of the listing with our free listing checker, which tests a title, item highlights and bullets against Amazon’s current rules.