How to Write ChatGPT Custom Instructions That Actually Help

Custom instructions should describe stable preferences, not a whole project. Include your preferred tone, formatting, level of detail, and rules such as “state uncertainty rather than guessing.”

Avoid adding private information, temporary tasks, or contradictory rules. Keep project-specific material inside a project or the opening prompt. Review instructions every few months; old preferences can create surprising answers.

Starter Example

Use plain English. Lead with the answer. For factual claims, name uncertainty
and suggest a primary source. Use short headings and practical examples.