The acronym INVEST helps to remember a widely accepted set of criteria, or checklist, to assess the quality of a backlog item.
If the backlog item fails to meet one of these criteria, the team may want to reword it, or even consider a rewrite (which often translates into physically tearing up the old story card and writing a new one).
I.N.V.E.S.T
Written well, an item in the Product Backlog has the following characteristics:
“I” ndependent (of all others)
“N” egotiable (not a specific contract for features)
“V” aluable (or vertically sliced)
“E” stimable (to a good approximation)
“S” mall (so as to fit within an iteration)
“T” estable (in principle, even if there isn’t a test for it yet)