Don'tAdd JSON output format rules — a fixed instruction is appended automatically after your text. Adding your own will conflict with it.
DoAdd a worked example (input → output). This is the single most effective way to get consistent formatting.
DoBe explicit about constraints you care about — title length, no dashes, UK spelling. Claude won't guess your house rules unless you state them.
DoUse the Assumptions: … trick — tell Claude to flag uncertain inferences at the end. Prevents hallucinated OE numbers.
Don'tOver-specify things Claude already knows well — "don't use American spelling" is enough.
DoIf descriptions keep coming out too long or too short, add a word count guideline (e.g. "40–60 words, one paragraph only").
DoTest with a product that has minimal DB data (just SKU + name) and one with rich fitment data — the prompt needs to work for both.