Here is how I used to change a prompt, and I suspect it's how you do it too.
Take a handful of real inputs — six felt like plenty, you can hold six in your head. Run the old prompt and the new prompt over them. Put the outputs side by side and read. One of them is visibly better. Ship that one.
This feels like evaluation. It has inputs, a comparison, and a decision. It is not evaluation, and it took me three consecutive prompt rewrites to notice.
The check that ended it
On a whim, I ran the same prompt twice over the same six inputs. Same model, temperature turned well down, nothing changed between the runs but the clock.
