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What is Custom instructions?

Updated July 21, 2026 · by Pedro

Custom instructions are ChatGPT’s persistent preferences. They set tone and defaults globally; they are not a substitute for task-specific Role/Stack/Specs/Constraints prompts.

Why does this term matter for AI prompts?

Precise vocabulary reduces vague instructions. When you name custom instructions correctly in a brief, Claude, Cursor, and GPT spend fewer tokens guessing. Pair definitions with structure on AI prompt builder and cost math on prompt token cost.

More glossary terms

Full list: prompt engineering glossary.

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