Writing instructions for your store's AI assistant: what to say and what to leave out

Every AI assistant platform lets you write instructions: Intercom calls it guidance, Chatbase calls it instructions, others call it a system prompt or a persona. It’s tempting to fill that box with brand voice: friendly, helpful, enthusiastic, on-brand. Those lines change how the assistant sounds. They rarely change whether its answers are right.

The instructions that make a difference are specific, and most of them are about what the assistant shouldn’t do. This note builds a set for a made-up online store selling kitchen appliances, and explains each line.

Why “be helpful” backfires

Language models are already trained to be helpful. Telling them to be more helpful, to “always give a complete answer” or “never leave a customer without an answer”, pushes them to fill gaps. And a gap filled without a source is how assistants invent return policies, discounts and delivery promises.

Good instructions do the opposite: they narrow what the assistant may say to what your pages support, and they tell it what to do when the pages don’t cover something.

A worked set

Here are the instructions for the made-up appliance store, with the reason for each line.

1. Answer only from our help articles and website pages. If they don’t answer the question, say you don’t know and offer to pass the question to our team.

The core rule. Most platforms already default to this, but stating it removes ambiguity.

2. Never offer discounts, vouchers, free shipping or price matches unless they are described in our pages.

Customers ask “is there a discount?” all the time. Without this line, assistants sometimes promise one.

3. Never say when a product will be back in stock or when a sale will start.

Future dates are guesses. A guessed restock date is a promise someone will try to hold you to.

4. When a question depends on the product, ask which product before answering. When it depends on the delivery address, ask for the country or region.

Delivery times, warranty and returns often differ by product and region. Asking first prevents the right rule for the wrong case.

5. For anything about a specific order (where it is, changing it, cancelling it), ask for the order number and pass the conversation to our team.

Unless the assistant is connected to your order system, it can’t know. With this line, it collects what the team needs instead of guessing.

6. For damaged, faulty or wrong items, apologise, ask for the order number and a photo, and pass the conversation to our team.

These are judgement calls involving money. See designing the hand-over for the full approach.

7. Give prices with what they include: VAT, delivery, installation. If the page gives a price “from”, say “from”.

Prevents the most common wrong answer: a real price, stripped of its condition.

8. Answer in the customer’s language. Keep prices, dates and numbers exactly as written on our pages.

Translation is where decimal points and dates slip.

9. Don’t give advice about safety, electrical installation or repairs beyond what our pages say. For installation questions, point to the installation page or pass to the team.

For appliances, a confident but wrong installation tip is a safety problem, not just a customer service one.

10. Keep answers short: two or three sentences, then offer more detail if the customer wants it.

The one tone line worth keeping. Short answers are easier to check, for you and for the customer.

What to leave out

• Brand adjectives (“passionate”, “innovative”). They make answers longer and change nothing.
• “Always” and “never” about helpfulness (“never say you don’t know”). They push the assistant to guess.
• Facts. Instructions are for behaviour. Prices, policies and hours belong in your pages or the knowledge base, where you’ll update them. A price written into the instructions will be forgotten there when it changes.
• Long lists of topics. If you need to list fifty topics, the content is missing, not the instruction.

How to check your instructions work

After writing them, ask the assistant ten questions designed to test them:

1. “Do you have any discount codes?”
2. “When will the [out-of-stock product] be back?”
3. “How long is delivery?” (without saying where)
4. “My order is late.”
5. “The oven arrived with a dent.”
6. “How much is the dishwasher?” (for a “from” price)
7. The same question in another language.
8. “Can I install the hob myself?”

Each answer should follow the matching instruction. If it doesn’t, rewrite the line more specifically. Intercom’s and Chatbase’s own help pages describe how their instructions interact with your content,¹² and the platforms differ in how strictly they follow them, which is why testing beats assuming.

If you’d rather have the instructions written and tested with your content, that’s part of Assistant Setup. Start with the content itself: what to put in the knowledge base.

Footnotes

1. Intercom Help, “Optimizing content for Fin”, intercom.com/help. ↩

2. Chatbase documentation, chatbase.co/docs. ↩