Backend search terms are the keywords you enter in a listing's "Search terms" field. Shoppers never see them. Amazon uses them, with the title and bullet points, to decide which searches the product can appear for.
The field is small, and it fails silently. Go over the limit and Amazon does not trim the extra — its guidance says the whole field is ignored. So the job is less about finding more keywords and more about choosing which few hundred bytes earn their place.
The rules Amazon publishes
These come from Amazon's Seller Central guidance on using search terms. Limits change, so confirm them in Seller Central for your marketplace before relying on them.
| Rule | What it means in practice |
|---|---|
| Under 250 bytes in most marketplaces | Japan allows 500 and India 200. The limit is in bytes, not characters |
| Over the limit, the field is not indexed | One byte too many costs you every term in it |
| Do not repeat what is already in the listing | Words in the title and bullets are already indexed. Repeating them wastes bytes |
| No brand names, ASINs or subjective claims | Neither yours nor a competitor's brand; no "best", "cheapest", "new" |
| Separate words with spaces | No commas or other punctuation needed |
Bytes are where non-English listings get caught. A plain Latin letter, digit or space is one byte. An accented letter such as é or ñ is two. A Japanese or Chinese character is three. A field that looks comfortably short in characters can be well over in bytes.
Nobody can read a competitor's backend field
Tools described as backend keyword "extractors" do not read the field. It is private to the seller's account, like a SKU.
What they do is a reverse lookup: they report the search terms a product has been observed ranking for. That is a different thing, and a more useful one. It shows what actually produces visibility, whichever part of the listing caused it. ASIN reverse keyword lookup explains what one request returns.
Filling the field in six steps
1. Reverse-look-up three to five competitors. Pick products close to yours in type and price.
curl --request POST \
--url https://ecommercedataapi.com/v1/amazon/traffic/keyword \
--header "Content-Type: application/json" \
--header "X-API-Key: ${ECOMMERCE_DATA_API_KEY}" \
--data '{
"marketplace": "US",
"asin": "B08CK5Z5Q1",
"page": 1,
"size": 50
}'Each row is a term the product appears for, with the fields you need to rank them:
| Field | Use |
|---|---|
keyword | The search term |
searches | Monthly searches for the term on the marketplace |
purchases, purchaseRate | Whether searches for it end in a purchase |
rankPosition | Where the product sits in organic results for the term |
conversionKeywordType | How the term converts for this product |
2. Merge and drop what does not describe your product. A term can be large and still wrong for you. Relevance is your judgment; no field decides it.
3. Drop brand terms. Competitor brands do not belong in the field under Amazon's rules.
4. Remove every word already in your title and bullets. Work at the level of words, not phrases. If your title has "stainless steel water bottle", the phrase "insulated water bottle" contributes one new word: "insulated".
5. Rank what is left and fill from the top. Order the remaining terms by purchaseRate and searches together, split them into words, keep each word once, and add words until you approach the limit. Leave a margin.
6. Count bytes, then save. Count in UTF-8 bytes, not characters.
How to decide which terms go in the title, the bullets and the backend in the first place is covered in how to optimize Amazon keywords. For the size of each term, see how to check Amazon keyword search volume.
Checking whether it worked
A few weeks after saving, run the reverse lookup on your own ASIN. Terms you added to the backend that now appear with a rankPosition are indexed and ranking. Terms that never appear are either not indexed or too competitive for the listing as it stands. Monitoring keyword rank covers doing this on a schedule.
What the backend field cannot do
It does not rank you by itself. Being indexed for a term makes you eligible to appear. Position depends on sales, conversion and relevance.
It does not replace the title. Terms in the title carry more weight and are visible to shoppers. The backend is for what did not fit.
It is not a place for terms you would not want in an ad. Irrelevant visibility brings clicks that do not convert.
Questions
How many backend keywords can I add? The limit is in bytes, not keywords: under 250 in most marketplaces according to Amazon's guidance. In English that is roughly 35 to 45 words.
Should I include plurals and misspellings? Amazon's guidance has said that variants such as plurals do not need repeating, so spend the bytes on different words instead. Confirm the current wording in Seller Central.
Can I see a competitor's backend search terms? No. You can see the terms they rank for through a reverse lookup, which is the more useful list.
Do I need commas between terms? No. Spaces are enough, and punctuation uses bytes.