How to write a great prompt

Last updated: May 6, 2026

Your prompt is the instruction manual for your AI assistant. Get it right and it will handle calls exactly the way you want — every time.

If you copied a prompt from ChatGPT — read this first

ChatGPT prompts are written for text conversations. fonio handles phone calls, which are faster, shorter, and need very different instructions. A ChatGPT prompt will often confuse your assistant or cause it to ignore key rules.

Where to find this in fonio

Step 1

Open Assistants in the left menu, then click the assistant you want to edit (e.g. "Lena").

Step 2

Under Advanced Abilities, click Custom Prompt / Instructions → Custom Prompts.

The 5 rules of a great fonio prompt

1 Start with who your assistant is

Give your assistant a role and a name. This sets the tone for everything that follows.

✗ Too vague"Answer calls for my company."

✓ Clear"You are Lea, the virtual receptionist for Müller Plumbing. You speak in a friendly, professional tone."

2 Use headers to structure your prompt

Use headers like Role, Conversation flow, and Important rules. This helps the assistant find and follow each section reliably.

✓ Clear

## Role · ## Conversation flow · ## If / Then rules · ## Important rules

3 Use If / Then sentences for every decision

Whenever the assistant needs to make a choice, write it as an If / Then rule. This removes ambiguity completely.

If the caller says it is urgent,

Then transfer immediately to +43 123 456 789.

If the caller asks about pricing,

Then "I'll have a colleague send you our pricing by email."

4 Tell it what TO do — not just what NOT to do

Negatives are harder for AI to follow reliably.

✗ Too vague"Don’t give out prices. Don’t promise callbacks."

✓ Clear"If asked about prices, say: I’ll have a colleague send you our pricing after the call."

5 Keep it under 300 words

Longer prompts don’t mean better results — they often mean worse ones. If your prompt is over 300 words, the assistant is more likely to skip or confuse instructions. Cut anything that isn’t essential.

Master Prompt — Build Individual Prompts

Mit dem fonio Master Prompt kannst du in wenigen Sekunden einen maßgeschneiderten Prompt für dich oder deine Kunden erstellen.

Here's how:

Open ChatGPT, Claude, or any other AI tool of your choice
Copy the fonio Master Prompt and paste it in
The AI will ask you a few questions about your use case — answer them briefly
Done: you'll get a ready-to-use, customized prompt that you can use directly in fonio

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