Describing a style takes paragraphs and still misses things. Showing it takes one example. This is few-shot prompting: including worked examples of input and the output you want.
Why showing wins
An example carries everything at once — tone, length, punctuation, how much detail, what gets left out, how edge cases are handled. You would have to write several paragraphs to describe all of that, and you would still forget something, because much of what makes output feel right is invisible until you see it violated.
Compare:
Write the summary in a neutral, professional tone, not too formal, around one sentence, starting with the subject rather than a verb, without a trailing full stop...
against simply showing two examples of exactly that.
Choosing examples that earn their place
The instinct is to pick clean, typical cases. That is the wrong instinct — those are the ones the model already handles.
Pick examples that carry the decisions:
- The case with a missing field, so the model sees what you want when data is absent
- The ambiguous case, so it sees which way you lean
- The case that looks like it should be handled one way but should not
- The shortest acceptable answer, which sets the floor
Two or three well-chosen examples beat six typical ones.
Roles change what gets noticed
A role is not decoration. "Review this as a security engineer" and "review this as a copy editor" over the same text produce genuinely different reviews, because the role changes what counts as worth mentioning.
Useful roles are specific about the perspective, not flattering about expertise. "You are a world-class expert" adds little. "You are the person who will have to maintain this code in a year" adds a lot, because it implies a set of concerns.
The cost
Examples are not free. They consume context, and in a long conversation they compete with the material you actually want the model to work on. Every example is tokens you are spending on instruction rather than content.
So use them where consistency matters — a format you will reuse, a house style, a classification task — and skip them for one-off questions where a sentence of description is enough.
The failure worth knowing
If your examples all share an accidental feature, the model will copy it. Three examples that all happen to be about finance can produce a finance-flavoured answer for an unrelated input. When output is subtly off in a way you cannot place, look at what your examples have in common that you did not intend.