Amazon backend keywords: how to use all 250 bytes

Backend search terms are the keywords shoppers never see. They sit in the Search Terms field of a listing (generic_keywords in flat files) and tell Amazon which other searches the product is relevant to. The field is small, the rules are strict, and most listings waste it.

The limit is bytes, not characters

Amazon allows fewer than 250 bytes in the search terms field. In plain English text a byte and a character are the same thing, which is why people talk about a “250-character limit”. They stop being the same as soon as you leave basic Latin letters:

A field of German or Japanese keywords fills up much sooner than its character count suggests. Count bytes, not characters.

The reason to be careful: if the field goes over the limit, Amazon may ignore all of it, not only the overflow. Staying at 249 bytes or fewer is the safe habit.

What belongs in the field

The field is for searches your visible copy does not already cover:

• Synonyms and alternative names for the product
• Long-tail variations of how people describe it
• Secondary uses and occasions
• Abbreviations and spelled-out forms

What does not

Amazon’s own guidance rules these out:

• Words already in the title, bullets or description. Amazon indexes those fields together with the search terms, so a repeated word buys nothing.
• Brand names, yours or anybody else’s, and ASINs.
• Subjective or temporary claims: best, cheapest, new, on sale.
• Punctuation. Separate terms with single spaces. Commas and semicolons are not needed and each one costs a byte.
• Plural and case variants. Amazon matches singular and plural, upper and lower case. You do not need both.
• Common misspellings. Amazon’s search corrects for them on the shopper’s side.
• Anything that is not true of the product. Irrelevant terms can get a listing suppressed.

A method for filling it

1. Collect the searches. Your own Search Query Performance report if you have Brand Registry, and the terms the top listings in your category rank for.
2. Write the visible copy first: title, Item Highlights, bullets, description.
3. List every word the visible copy already uses and strike those words from your keyword list.
4. Remove duplicates inside the list, then plurals of words you already have.
5. Order by value, most important searches first, and cut from the end until the byte count is 249 or lower.
6. Lowercase everything and join with single spaces.

Step three is the one people skip, and it is where most of the wasted bytes come from. A multivitamin whose title already says Multivitamin, Men and Tablets gains nothing from repeating them in the backend.

Example

The visible copy of a men’s multivitamin already covers multivitamin, multimineral, men, daily, tablets, energy, immune, heart, allergens. A backend field that adds something:

adult male vitamins over 40 over 50 wellness nutrition mineral complex everyday essentials long lasting bottle

110 bytes, no word repeated from the title or highlights, no brands, no punctuation. There is room for about twenty more words.

Checklist

• 249 bytes or fewer, measured in bytes
• No word that already appears in the title, Item Highlights, bullets or description
• No brands, no ASINs, no competitor names
• Spaces only, all lowercase
• Every term is true of the product

Where Cobalt12 fits

Cobalt12 writes the backend field last, after the title and bullets, from the competitor audit of your category. It counts bytes rather than characters and flags any term the visible copy already indexes. You can try it on your own product; the first listing is free.

This article reflects Amazon’s published guidance as of September 2026. Limits can differ by marketplace, so check Seller Central help for yours.