The short version

A negative instruction removes one option but often leaves many alternatives unclear. “Do not use markdown” does not say whether the answer should be flowing prose, a table, labeled fields, or something else. A positive target gives Claude a destination.

Anthropic’s prompting guidance recommends telling Claude what to do, describing the desired format in detail, and recognizing that the style of the prompt itself can influence the response.

Positive target, allowance, boundary

A compact way to design formatting instructions is:

  1. Positive target: Describe the intended structure, tone, and reading experience.
  2. Allowance: Explain when an alternative format is genuinely useful.
  3. Boundary: Prohibit the patterns that would materially harm the result.

For example:

Write a concise management commentary in three short prose paragraphs. Connect the movement, likely driver, and recommended action naturally. Use bullets only for genuinely discrete actions. Do not repeat the same explanation in multiple sections.

This gives Claude a default form, a sensible exception, and one clear limit.

Why positive instructions work

Prohibitions can accumulate into a maze: do not be long, do not use many headings, do not repeat, do not sound mechanical. Claude must infer what remains. A positive specification collapses those restrictions into a coherent result: concise connected prose with a clear progression and limited structure.

Positive instructions are also easier to review. A teammate can judge whether “three short paragraphs for an executive reader” matches the product. A list of things to avoid is harder to translate into a shared quality standard.

Match the prompt to the output

If you want flowing prose, write the instruction in clear sentences rather than surrounding it with dozens of tiny bullet points. If you want a structured record, present the fields in the order they should appear. Examples can further demonstrate tone and density, especially when formatting matters more than abstract rules can express.

Boundaries still have a place. Use them for important constraints such as excluding unsupported claims, sensitive data, or extra text around a machine-readable object. The point is not to eliminate negative rules; it is to anchor them in a clear positive outcome.

Practical checklist

  • State the preferred form first.
  • Describe tone, length, and audience concretely.
  • Use an example when the desired style is subtle.
  • Allow alternatives only when they improve clarity.
  • Reserve prohibitions for material boundaries.
  • Make the prompt’s own style compatible with the requested answer.

Try it

Rewrite “do not make the report too long, do not use many headings, and do not repeat yourself.” Specify the number and purpose of sections, the desired reading experience, one allowed exception, and one necessary boundary.