WhatsApp auto-reply bot for small businesses: the three kinds, what they cost, and how to set one up

A WhatsApp auto-reply bot answers customer messages on your number without you typing. There are three different things people mean by that: the built-in greeting and away messages in the WhatsApp Business app, which send fixed text; keyword bots, which match words to canned answers; and AI bots, which read the whole message and answer from your own prices, hours and policies. They cost different amounts and fail in different ways, so this guide treats them separately before showing a ten-minute setup for the one most small businesses actually need.

What kinds of WhatsApp auto-reply are there?

Speed is why any of the three exists. In the InsideSales.com and MIT lead response study, contacting a web lead within five minutes rather than thirty made contact 100 times more likely and qualification 21 times more likely (Oldroyd, MIT, 2007). A small business cannot staff that window by hand at 11pm, which is the gap each of the three below tries, with very different success, to fill.

The built-in replies are worth switching on today regardless. They are free and they stop a customer thinking you have vanished. They just do not answer anything.

What an AI auto-reply bot can answer

From a knowledge base of your own material, an AI bot handles the questions that make up most of a small business's inbox:

• Price, stock and availability for named products or services, including "is the queen size in stock" and "how much for two sessions a week".
• Hours, location, delivery areas and charges, including same-day cut-offs.
• Booking requests: it collects the service, day, time and contact and logs them to a Google Sheet or a booking link for a human to confirm.
• Policies: returns, deposits, cancellation, payment methods.
• Voice notes and photos: a customer who sends a voice message in Bahasa Malaysia asking about an item, or a photo of a receipt or a product, gets an answer in the same language.

What it should not do is invent. The setup below assumes the bot is told to answer only from your documents and to say it will check with the team otherwise, which is how Replai is configured by default.

Setting one up in ten minutes

1. Use a dedicated business number. Not your personal one. If the number is new, let it exist on WhatsApp with normal manual use for a week or two before adding a bot.
2. Write the knowledge base first. Prices, hours, delivery, policies, the ten questions you answered most last week. Paste it as text, a URL or a PDF. This is the whole job; everything else is clicks.
3. Set the tone and the hand-off rule in the system prompt: which language to reply in, what it must never invent, when to pass to a human. We keep a system prompt guide with copy-paste examples.
4. Pair the number by scanning a QR from WhatsApp → Linked devices. On Replai the bot starts on new conversations only, so the chats already on the phone are untouched.
5. Test with real questions from another phone. Fix the documents, not the prompt, when an answer is wrong.
6. Turn on lead capture to a Google Sheet so the bot's work is visible to staff.
7. Read every conversation for the first week. That is where you learn what is missing from the knowledge base.

What it costs in 2026

Bots that pair to your existing number charge a flat monthly fee with no per-message cost, because they do not use Meta's Business API. Replai is $19 a month for one number and 120 conversations a cycle, $49 for up to three numbers, 300 conversations and outbound campaigns, and $99 for five numbers and 600. A conversation is one customer thread of up to five bot replies; top-ups are 100 conversations for $9, or $8 on Growth and $7 on Pro; the 7-day trial needs no card.

Tools built on the official WhatsApp Business API, such as Wati, Respond.io and Interakt, charge a subscription and pass Meta's per-message fees through on top. That route makes sense for large outbound broadcasts; for answering inbound on one or a few numbers it is usually the more expensive way to do the same job. The fee layers are broken down in what the WhatsApp Business API actually costs, and the two connection methods are compared in WhatsApp chatbot without the Business API.

When should you not use an auto-reply bot?

• You have no written prices or policies. Write them first; a bot cannot answer from nothing.
• Your messages are mostly existing customers mid-conversation. Keep the bot on new conversations only, or skip it.
• You send bulk marketing. A linked-device bot is deliberately throttled and WhatsApp restricts numbers that blast; use the official API for that.
• A restriction would end your business. Linked-device bots are unofficial. Read our honest answer on ban risk before deciding.

Related

• How to write a system prompt for a WhatsApp customer service bot
• WhatsApp auto-reply for Malaysian small businesses: the 2026 guide
• A starter WhatsApp assistant for any small business (use case)