tools-only Negation and Negative Instructions
Opus: Processes negative instructions ("don't include X") reliably. Understands complex negations and double negatives.
Haiku: Negative instructions are less reliably followed than positive ones. "Don't use bullet points" may still produce bullets. Complex negations ("never fail to include") can be misinterpreted.
Mitigation: Reframe every negative as a positive directive.
BAD: Don't use jargon.
GOOD: Use plain language that a high school student would understand.
BAD: Never include personal opinions.
GOOD: State only facts supported by the provided data.
BAD: Don't forget to include the date.
GOOD: Include the date in YYYY-MM-DD format on the first line.
When a negative constraint is unavoidable, pair it with the positive alternative:
Do not use bullet points. Instead, write in flowing prose paragraphs.
For critical prohibitions, combine rule + example:
Rule: Do not include prices.
Example output shows: "Contact sales for pricing." (not "$99/month")