Amazon backend keywords provides up to 5,000 characters to customize. But how best to use them?
What you don’t want to do, is to think of these backend keywords like the old <meta> keyword tags in HTML, and just try stuffing everything you can think of into them.
You want to ensure your main Amazon keywords are in at least your product name, features (bullet points) or description
Especially your money keywords. For example, if you sold garlic presses, you’d want to prioritize putting popular keywords like ‘garlic press’, ‘garlic mincer’ and ‘garlic squeezer’ into your listing.
At which point, the backend keywords should be for any keywords you don’t have in your listing. There’s no need for duplicates.
Amazon explains this via the help section of their site: