Build an inventory and sales (POS) app for a small shop

Shop owners keep stock in their heads and sales in a notebook until the day both fail at once. A small inventory-and-sales app fixes that without an ERP: products, quantities, a quick bill, and a daily total. On App Builder Agent, this is a one-evening build that thousands of shopkeepers have asked for in one form or another.

This guide covers the flow from product list to daily report, the credit (udhaar/khata) ledger many markets need, and how to keep it usable on a cheap Android phone at the counter.

What the counter app needs

Speed at the counter is everything. Design around a bill that takes ten seconds:

• Products with quantity and prices — Name, buy price, sell price, unit, current stock, optional barcode or SKU.
• Quick billing — Search or tap products, quantities, discount, total, cash/UPI/credit, print or share the receipt.
• Stock in / stock out — Purchases increase stock, bills decrease it; a manual adjustment for breakage.
• Low-stock alerts — A threshold per product and a list of what to reorder.
• Customer credit ledger — Customers, amounts owed, payments received, a reminder button that opens WhatsApp.
• Daily and monthly reports — Sales, profit (sell minus buy), top products, credit outstanding.
• Backup — Export to CSV/JSON; a lost phone must not mean lost accounts.

Build it with App Builder Agent, step by step

Start with products and billing; add credit and reports once the first week of bills is in.

1. Create a mobile app project. The app lives on the shop phone or tablet; an APK is what you want.
2. Describe the shop and the bill flow. Paste twenty real products so names and units are right from the start.
   Build an inventory and billing app for “Rahman General Store” (grocery, Dhaka). Products with buy price, sell price, unit (pc/kg/litre), stock and low-stock threshold. Billing screen: search products, tap to add, quantity, discount, total, payment cash/bKash/credit, share receipt as text. Stock in screen for purchases. Customers with credit ledger and “remind on WhatsApp”. Reports: today, this month, profit, low stock. Bengali and English labels. Everything stored on the device.
3. Make a few bills in the simulator. Check that stock decreases and totals are right. Say “make the product buttons bigger” or “remember the last customer” if needed. Bill the same item past zero stock and see what happens — it should warn, not go negative silently — and try the camera in the Simulate panel if you asked for barcode scanning.
4. Add reports and backup. Monthly profit, top products, an export button.
   Add a Reports tab with a daily sales chart for the last 30 days, top 10 products by profit, and total credit outstanding. Add Export to CSV that shares the file.
5. Install at the counter. Export the APK; if two people bill at once, ask for a hosted backend so both phones share the same stock.

Prompts that work well

Different trades, different words — the shape is the same:

Common mistakes (and the fix)

• Editing stock directly instead of recording movements. If stock is a number you overwrite, you can never explain why 40 became 31. Ask for every change to be a movement (purchase, sale, adjustment with reason) and for current stock to be the sum. Reports then come for free.
• Profit calculated from today’s buy price. Rice bought at ৳62 last month and ৳68 this week should not show the same margin. Store the buy price on each purchase and on each bill line, so profit reports stay honest when suppliers raise prices.
• Duplicate products from typos. “Sugar 1kg”, “Sugar 1 kg” and “sugar1kg” split your stock three ways. Ask for a duplicate check on name when adding a product and a merge tool in admin.
• Negative stock without warning. Billing past zero happens when a purchase was never entered. Warn at the counter, allow it with a tap, and list “negative stock” items in the reorder report so the missing purchase gets recorded.
• Credit with no reminder trail. A khata that only stores the balance leads to arguments. Record each sale and payment with a date, show a statement per customer, and make the WhatsApp reminder include the statement text.
• Two phones with on-device data. The moment a second counter or the owner at home needs the numbers, device storage silently forks the data. Ask for a hosted backend before the second phone, not after, and keep offline billing with a sync when back online.

Make it feel finished

• Big product buttons, minimal typing: the counter is busy.
• Ask for receipt sharing as text first; printing comes later and varies by printer.
• Log the buy price at the time of purchase so profit stays right when prices change.
• Add a PIN lock for reports and stock edits when staff use the phone.

Installing, publishing and next steps

A single-phone shop needs no server: everything stays on the device and exports to CSV. Download APK in the Preview tab gives you a release-signed test build to install on the counter phone the same evening; the APK app builder page covers signed store builds with your own package id if you ever want the app on the Play Store for several branches. When a second counter or a remote owner needs the same numbers, ask the agent for a hosted backend — the platform provisions the database and API for the project and the app syncs through it. Payments inside the app (bKash, UPI, cards) can only be simulated; real collection stays at the counter. The first app is built free; the AI app builder page shows what the $1.49 Member plan and the paid plans add.

The ready-made inventory & sales apps gallery shows several billing screens built for cheap phones. If invoices with GST or VAT fields matter more than stock, read the bill and invoice app guide; if you also pay daily-wage staff from the same till, the daily wages and attendance app guide fits alongside. Keep the project; every new report or field is one message away. Open the builder and paste twenty products.

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