Make a bill and invoice app for your small shop (no code)

A kirana store in Pune, a mobile repair counter in Lucknow, a tailoring shop in Surat: all of them write bills by hand or on a photocopied pad, and all of them lose money to the same three things — forgotten credit (“udhaar”), wrong GST on the receipt and a month-end total that nobody can reconstruct. A billing app fixes those, but the ones on the store are either built for distributors with a thousand SKUs or lock your own sales data behind a yearly fee.

Describing the app to App Builder Agent gets you something narrower and more useful: your products, your tax rates, your shop name on the PDF, a PIN so the helper can bill but cannot see the monthly total. The AI agent writes the React Native code, you test it in the browser preview, then install the APK on the shop phone. This guide walks through what to ask for, in what order, and the mistakes that make a billing app untrustworthy.

What a billing and invoice app must handle

• Product list with price and tax slab — Each item carries its GST rate (0, 5, 12, 18 or 28%) so the invoice computes itself.
• Fast item entry — Search by name, tap to add, quantity stepper; a bill at the counter must take under thirty seconds.
• Customers and credit — Name, phone, running balance; udhaar is half of small-shop accounting.
• Invoice numbering that never repeats — Sequential, per financial year, and never reused after a delete.
• Tax breakdown on the invoice — CGST/SGST split for local sales, IGST for inter-state, and an HSN column if you file returns.
• PDF, print and share — A PDF that looks right on A4 and on a 58 mm thermal printer, shared to WhatsApp in one tap.
• PIN lock and roles — Staff can create bills; only the owner sees totals, edits prices or deletes.
• Monthly summary — Sales, tax collected, outstanding credit, top products; the numbers your accountant asks for.

Build it with App Builder Agent, step by step

1. Start a mobile app project and keep the data on the phone. A single-counter shop does not need a server; on-device SQLite means bills work when the broadband is down and nothing leaves the shop. If you later open a second branch, ask for a hosted backend and the agent moves the data across.
2. Describe the shop, the tax rules and the screens. Give real product names and prices; the agent uses them as seed data and gets the rounding right.
   Build a billing app for “Shree Ganesh General Store”, Pune, GSTIN 27ABCDE1234F1Z5. Products with name, price, unit (pc/kg/ltr) and GST rate (0/5/12/18%). Seed 15 products such as Amul Butter 500 g ₹275 (12%), Tata Salt 1 kg ₹28 (5%). Screens: New Bill (search products, add with quantity, choose customer or walk-in, cash/UPI/credit, discount in ₹ or %), Bills list with date filter, Customers with balance and a “collect payment” button, Products, Reports (today and this month: sales, GST collected, outstanding credit). Invoice numbers GS/25-26/0001 onwards. Invoice PDF with CGST/SGST split, print and share to WhatsApp. 4-digit PIN on launch; reports and product edits need the owner PIN. Store everything in SQLite on the device. Saffron and white design, large buttons.
3. Make a few bills in the preview. Add three items with different tax rates, apply a 10% discount, pick a credit customer, then open the PDF. Check the tax lines by hand once: for an 18% item at ₹100 the invoice must show ₹9 CGST and ₹9 SGST, and the total must round to the nearest rupee with the rounding shown as its own line. If anything is off, paste the numbers to the agent.
4. Add the credit flow properly. This is where most home-made billing apps stop short.
   On the customer screen show every credit bill and every payment as a statement with a running balance. “Collect payment” accepts partial amounts and lets me pick which bills it settles. Add a “Send reminder” button that opens WhatsApp with a message containing the customer’s name, balance and my UPI ID.
5. Install it on the shop phone. Download the test APK from the Preview tab, install it on the counter phone, pair the thermal printer over Bluetooth and print a real bill. Keep the browser project open — every later change is a message, and a fresh APK is a click.

Prompts that work well

The same structure carries over to shops that bill differently. Change the fields, not the shape.

Common mistakes (and the fix)

• Storing prices as decimals. Floating-point totals drift by a paisa and the accountant notices. Ask the agent to store amounts in paise as integers and format them for display.
• Editable invoices after they are shared. Once a PDF has gone to a customer the numbers must be frozen. Ask for a “cancel and re-issue” flow that creates a credit note rather than editing in place.
• Tax added to a discounted total instead of per line. GST applies per item at its own rate; a bill-level discount must be spread across lines proportionally. State this explicitly in a follow-up prompt.
• No backup. A phone that falls into a bucket takes the year with it. Ask for a weekly “Backup to file” that exports a JSON and shares it to Google Drive or WhatsApp, and a matching Restore button.
• Searching only from the start of the name. Staff type “butter”, not “Amul”. Ask for search that matches anywhere in the name and in a short code you assign.
• A PIN that can be bypassed by force-closing. Ask for the PIN check on every launch and after five minutes in the background, not only on first open.

Make it feel finished

• A large “New Bill” button on the home screen, reachable with a thumb, with today’s sales total beside it.
• Your logo, address, GSTIN and a “Thank you, visit again” line on the PDF, plus a UPI QR code so customers can pay from the receipt itself.
• A quantity stepper with plus/minus and a keypad for weights like 0.250 kg.
• Hindi and Marathi labels alongside English if your staff prefer them; the agent can add a language switch in Settings.
• An “end of day” screen: cash expected in the drawer, UPI received, credit given, one tap to share the summary to the owner’s WhatsApp.

Installing, publishing and next steps

Everything above runs in the browser preview first — the Simulate panel even lets you test the print and share sheet without a printer. When it behaves, the test APK from the Preview tab goes straight onto the shop phone; the AI app builder page explains what is free (your first build) and what the $1 permanent membership unlocks (unlimited test APKs and source export). If you want the app on the Play Store for a chain of shops, ask for a signed APK and AAB with your own package id — the keystore is kept with the project.

For stock alongside billing, browse the ready-made inventory & sales apps, then read the inventory and sales guide for purchase entries and low-stock alerts, and the daily wages and attendance guide if you also pay helpers by the day. Open the builder, paste the prompt from step 2 with your own shop name, and you will be printing your first bill this afternoon.

Frequently asked