How do I set a custom instruction?
A paid plan is required to save Custom Instructions or use Smarter. Free users can still use formulas with the default settings.
- 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?
Repeated requests can reuse a cached response instead of making a new AI request. A cache hit saves usages, but cached responses are temporary and may not always be available.
- For a fresh answer, open Custom Instruction and click Clear Cache, then rerun your formula. Changing the prompt is another option.
- Clearing the cache does not rerun formulas automatically or save their results permanently.
Frequently Asked Questions
Do I need a paid plan for Custom Instruction?
A paid plan is required to save Custom Instructions or use Smarter. Free users can still use formulas with the default settings.
Does cache affect results?
A cached response can repeat an earlier answer. To request a fresh answer, click Clear Cache and rerun the formula, or change the prompt. Cache is not permanent storage for your results.
Where can I see all formulas?
See Formula reference for the full list and examples.