How do I set a custom instruction?
- In Google Sheets, go to Extensions → AI for Sheets → Custom Instruction.
- Add a Global Instruction (applies to your account) and optionally a Sheet Instruction (applies to the current spreadsheet).
- Click Save.
Examples you can copy
- Keep the response under 50 words.
- Return only a single sentence, no bullet points.
- Return JSON with keys: name, email, company, notes.
- Use Australian English and a friendly, professional tone.
What is Default vs Smarter?
In Custom Instruction → Text Formula, you can choose between:
- Default 1x: faster and cheaper, good for most tasks.
- Smarter 5x: better reasoning, but costs more usages per call.
If you see timeouts, switch back to Default and shorten your prompt or reduce the range you pass into the formula.
How do image formulas work?
=IMAGEN and =EDIT use Gemini 2.5 Flash Image. There is no image model selector in Custom Instruction.
Image generation and editing cost 50 usages per call.
How does cache work?
When Cache is on, repeated prompts can return the same response instead of making a new request. This helps save usages when you are filling down many rows or re-opening a sheet.
- Turn Cache on in Custom Instruction → Cache.
- If you want a fresh answer, change your prompt slightly or click Clear Cache.
Frequently Asked Questions
Do I need a paid plan for Custom Instruction?
Custom Instruction and Smarter mode are included in paid plans. If you are on the free plan, you can still use the formulas, but advanced settings may be locked.
Does cache affect results?
Cache is meant to return the same answer for the same prompt so results stay stable. If you want variety, turn Cache off or change the wording of the prompt.
Where can I see all formulas?
See Formula reference for the full list and examples.