In short
Write for the decision the shopper is trying to make, then check that the page contains the words they would have typed. In practice that means opening with what the product is and who it suits, putting the attributes people search with into the first hundred words, covering fit, compatibility and care in plain language, and never reusing the same paragraph across products. Length is set by how complicated the purchase is, not by a word target, and the description has to be readable in the page HTML rather than loaded by a script.
Begin with the question that brought the shopper here
Every product page is read by somebody trying to settle one thing. Will this fit my bike, will it suit my skin, is it warm enough for a Canadian winter, will it hold a laptop and a change of clothes. Write that answer in the first two sentences and the rest of the page becomes easier, because you know what it is supporting.
The search terms follow naturally from that. A description written around the decision contains the words the decision is made in, and those are the words people search with: the measurement, the material, the compatibility, the use case, the season. A description written around a keyword tends to say the keyword several times and answer nothing.
Get the specifics from three places rather than from imagination. The supplier's technical sheet gives measurements and materials, the customer service inbox gives the questions people ask before buying, and the reviews give the language buyers use afterwards. Those three sources between them contain almost everything the page needs.
One consequence: the best product copy is often shorter than expected. A well-known consumable might need eighty words. A piece of equipment somebody researches for a month might need six hundred, plus a table.
A structure that works on most product pages
Put the two lines that answer the buying question above the fold, next to the price and the buy button. Follow with a short scannable block of the facts that decide the purchase: dimensions, weight, materials, capacity, compatibility, what is in the box, and whatever your category treats as a specification.
Below that, use headed sections for the depth. How it is used, how it is cared for, how to choose between it and the neighbouring option, and sizing or fitment detail where the category needs it. Headed sections make the page skimmable, give search engines a structure to read, and let you answer a question at the point it comes up rather than in a wall of text.
Keep the whole thing in the page HTML. Descriptions that live inside a tab widget that fetches content on click, or inside an app that renders after load, may not be seen at all. Confirm with the URL inspection tool rather than trusting the browser.
Finally, write the title tag and the H1 to name the product plus the attribute that distinguishes it. Brand, product name and the defining feature reads better and matches more queries than a name alone.
Where the search terms actually belong
Concentrate on four places and stop worrying about density. The title tag and H1 carry the product name and its defining attribute. The opening paragraph carries the same phrase in a natural sentence plus the obvious variant of it, since shoppers search with and without brand names. The specification block carries model numbers, part codes, sizes and compatible products, which are exactly the strings people paste into a search box. Image alt text describes what is in the picture, including the colour or configuration shown.
Synonyms matter more than repetition in ecommerce, because categories carry regional and generational vocabulary. Trainers and sneakers, torch and flashlight, hob and cooktop, chesterfield and sofa. Use the one your market uses in the visible copy and let the other appear naturally where it fits, such as in a comparison line or an FAQ.
Avoid stuffing lists of related keywords at the bottom of the page. They add nothing, they read badly to a shopper who scrolls, and they make the page look assembled rather than written.
One more place is worth attention: the internal links inside the description. Linking a compatible accessory, a matching item or the parent category with descriptive anchor text builds the structure crawlers use and lifts basket size at the same time.
Doing this across a catalogue without duplicating yourself
At any scale, the practical method is structured data in, written text out. Get the attributes into clean fields first: dimensions, materials, fitments, care instructions, country of origin, certifications. Once those exist as data, the copy can be assembled per product with the specifics filled in, and no two pages end up saying the same thing because no two products have the same values.
Drafting with a language model is reasonable when it is working from those verified attributes and a human reviews the output. It is not reasonable when it is asked to invent benefits, because it will produce claims you cannot support, and in regulated categories such as supplements, skincare and anything making a health or safety claim, that is a legal problem rather than a quality one.
Prioritise by revenue. Rewrite the products that already receive impressions and sessions before the long tail, then work down. On a catalogue of thousands, the first hundred descriptions usually cover a large share of the traffic that is in reach.
And keep a rule for supplier copy: it is a starting point for the specification block, never the whole page. What you add on top is what makes the page yours, and it is also what makes it useful to somebody choosing between three retailers who all pasted in the same text.
Related questions
How long should a product description be?
As long as the decision requires. Simple, familiar products can be handled in a short paragraph plus specifications, while considered purchases need sizing, comparison and care detail that can run to several hundred words. Word count is not a ranking factor, so the useful question is whether a shopper could decide from the page without opening another tab.
Can a language model write product descriptions for a store?
It can draft them from verified product attributes, and that is a sensible use at scale. It should not be asked to generate claims, benefits or specifications it cannot source, and everything it produces needs review before publication. In regulated categories the review has to include whoever is accountable for the claims being made.
Does using the same description on several products cause a problem?
There is no penalty for it, but the pages give search engines no reason to prefer one over another, so they tend to compete with each other and one gets filtered out of results. It also gives shoppers nothing to choose on. Vary the copy by the attributes that actually differ, which is why clean attribute data matters.