How to Write a Good Prompt for Your WhatsApp Sales Assistant

If you use an AI assistant to respond to your business's WhatsApp messages, you already know that the quality of the responses depends a lot on how well you explain what to do. That's what we call a "prompt": the instruction you give to the AI. It's not the same as saying "reply to messages" as it is giving detailed instructions about your business, tone of voice, and what to do in each situation. In this article, we show you how to write prompts that work.

What is a prompt and why does it matter?

A prompt is basically an instruction you give to the AI. It can be a question, a set of rules, or a description of what you expect it to do. In the context of a WhatsApp sales assistant, your prompt is what tells the AI how to behave, what information to use, how to talk to your customers, and when to escalate to a human.

The difference between a vague prompt and a well-crafted one is huge. A vague prompt generates generic, confusing responses that don't represent your brand. A clear and specific prompt ensures the AI understands your business, your tone, and your goals, and that the response suggestions are truly useful.

The key elements of a good prompt

• Business context: what you sell, to whom, and what problems you solve
• Tone and personality: how you want the AI to speak on behalf of your brand
• Relevant information: data about products, prices, policies, hours
• Limits and restrictions: what it should NOT do, when to escalate to a human
• Clear objectives: what you want to achieve in each conversation (sell, inform, retain)

Step by step: how to structure your prompt

1. 1Introduce your business in one or two sentences. Example: 'We are an online store of sports clothing for women. We sell local and international brands with shipping nationwide.'
2. 2Define the tone. Formal or friendly? Fun or serious? Example: 'Speak in a warm, close, and friendly tone. Use emojis occasionally. Avoid jargon that a new customer wouldn't understand.'
3. 3List your key information: main products, prices (if possible), business hours, return policies, payment methods.
4. 4Explain your objectives. Example: 'The goal is to help the customer find what they're looking for, answer questions about products, and facilitate the purchase. If the customer wants to make a return, offer to transfer them to an agent.'
5. 5Define when to escalate. Example: 'If the customer is angry, asks to speak to a human, or asks a question you can't answer with the information you have, offer to transfer them to a sales agent.'
6. 6Add concrete examples. If you can, show how you want it to respond in typical situations. The AI learns better with examples.

Common mistakes when writing prompts

• Being too vague: 'Respond like a salesperson' doesn't give enough information. Be specific.
• Forgetting context: AI doesn't know what you sell unless you tell it. Include details.
• Not setting limits: if you don't tell it what NOT to do, it can make mistakes. Be clear about restrictions.
• Very long and confusing prompts: AI processes clear, organized instructions better. Use bullet points and structure.
• Not updating the prompt: if something in your business changes (new product, schedule, policy), update the prompt. Otherwise, AI will continue with outdated information.
• Ignoring tone: if your brand is fun but you give it a formal prompt, AI will sound out of place.

Example of a well-crafted prompt

Here's an example you can adapt to your business:

"You are the sales assistant for Café Artesano, a small coffee shop in Palermo that sells specialty coffee and homemade desserts. Your tone is warm, friendly, and approachable. Respond in Argentine Spanish, without being too formal. You can use emojis occasionally (☕, 🍰). Our main products are: Espresso Coffee ($150), American Coffee ($120), Croissants ($80), Chocolate Cake ($250). We are open Monday to Friday from 8:00 to 18:00, Saturdays from 9:00 to 17:00, closed on Sundays. We deliver within the Palermo area (up to 2 km) at no charge. If the customer asks about deliveries to other areas, offer to coordinate and charge for shipping. If someone asks for something we don't have, suggest alternatives. If the customer is upset or asks to speak to a manager, offer to transfer to a human. Don't invent information about products or prices you're not sure about."

How to improve your prompt over time

A prompt is not something you write once and that's it. It's a living document that needs to be reviewed and improved.

• Review the responses generated by the AI. Is there something you don't like? Adjust the prompt.
• Pay attention to the questions you frequently receive. If there's something the AI doesn't answer well, add information to the prompt.
• Ask your team for feedback. If human agents see the AI saying something odd, it's a sign that the prompt needs adjustments.
• Test small changes. Don't change everything at once; make gradual adjustments and observe the results.
• Update information regularly. If you launch a new product, change hours or policies, update the prompt.

Practical tips for writing better

• Use clear and direct language. Avoid unnecessary jargon or confusing phrases.
• Be specific with numbers. Instead of 'affordable prices', state the exact prices.
• Include conversation examples. Show how you want it to respond in real cases.
• Organize information into sections. This helps the AI process better and makes it easier to update later.
• Think about the customer. What do they need to know? What matters to them? That should be in the prompt.
• Be honest about limitations. If the AI can't do something, better to say so than to let it make things up.

Writing a good prompt is a skill that improves with practice. Don't expect it to be perfect on the first try. The important thing is to start with something clear and specific, observe how it works, and adjust as needed. With a well-crafted prompt, your AI assistant will be much more useful for your business, and your customers will have a better experience on WhatsApp.

Second-order questions: what happens after you write your prompt

Once your prompt is ready, questions arise that you didn't think of at first. For example: what if the customer writes in another language? What if they ask for something that's not on your product list? How do you handle a conversation that goes off on tangents?

The short answer is: the prompt doesn't solve everything. That's why serious tools combine the prompt with business rules and human oversight. At Wando, for example, the AI suggests responses and your team approves them with a click. That gives you control without having to program every scenario.

Another common question is whether the prompt replaces a human agent. Not entirely: the AI speeds up responses and handles simple queries, but delicate situations (angry customers, complaints, complex questions) need a person. Your prompt should make clear when to escalate, and your team needs to be prepared to take over those conversations.

Lastly, think about evolution. Your prompt today won't work next year. Products change, schedules change, your brand tone evolves. Reviewing it regularly is not optional; it's part of maintaining your assistant.

• Define what happens with messages in other languages or outside business hours.
• Establish a clear process for escalating conversations to humans.
• Schedule periodic reviews of the prompt; don't leave it static.

Concrete example: from a vague prompt to an effective one

Let's look at a real case. An aesthetics business writes: "Respond to WhatsApp messages in a friendly way and offer appointments." That prompt is so generic that the AI doesn't know what services you offer, how much you charge, or what coverage areas you have.

Now, look at this improved version: "You are the assistant for Belleza Total, an aesthetics center in Caballito. We offer manicures ($800), pedicures ($900), and laser hair removal ($1200 per session). Our tone is warm and professional. Respond in Rioplatense Spanish. We operate Monday to Saturday from 9:00 to 18:00. If someone requests an appointment, offer available times and confirm with the client. If they ask about prices, provide the updated list. If the client wants a service we don't offer, suggest alternatives. If there's a complaint or something you don't know, transfer to a human agent. Don't make up information."

The difference is enormous. The first prompt leaves everything to the AI's imagination. The second gives it context, concrete data, tone, and limits. The result: useful responses, consistent with your brand, that don't invent prices or services.

Adapt this example to your business. It doesn't need to be perfect on the first try; start with what you know and adjust over time.

Common mistakes and how to avoid them

Error number one is thinking that AI reads your mind. If you don't give it context, it will improvise. Another classic: not setting boundaries. If you don't tell it what NOT to do, it could promise things you can't deliver, like discounts that don't exist or deliveries you don't make.

There's also the mistake of overloading the prompt. You want AI to know everything, but a mile-long, messy prompt confuses more than it helps. Organize information into clear sections and prioritize what's really important.

A very common mistake in practice: not updating the prompt when something changes. If you launched a new product or changed your schedule, AI will keep responding with outdated data. And that shows, and the customer notices.

The solution is simple: treat the prompt as a living document. Review it monthly, adjust what doesn't work, and test small changes. Don't be afraid to iterate: AI is flexible, and you should be too.

• Don't assume AI knows your business: give it context.
• Set clear boundaries on what AI should not do.
• Update the prompt when your business changes.
• Organize information to avoid overwhelming AI.

How to measure if your prompt works

It's not enough to write a good prompt: you need to know if it's working. The most direct metric is the response approval rate. If you approve most of AI's suggestions in Wando, it's a sign the prompt is aligned with your style. If you reject them often, adjustments are needed.

Another useful metric is response time. If AI saves you minutes in each conversation, the prompt is fulfilling its goal. Also look at customer satisfaction: if you receive fewer complaints and more resolved inquiries, you're on the right track.

Pay attention to error patterns. Does the AI invent prices? Does it give overly long answers? Does it fail to scale when it should? Each pattern tells you which part of the prompt needs more clarity. For example, if it invents prices, add a line that says "do not invent prices, use only the ones I give you."

Finally, compare with a human team. If agents resolve queries that the AI cannot, that is an opportunity to improve the prompt with that information. The AI does not replace your team: it empowers it.

• Approval rate of suggested responses.
• Average response time.
• Recurring error patterns.
• Comparison with resolution by human agents.