InvoiceApp — Offline Invoicing and Stock Control

Small shops run on a monthly subscription they resent, or on a spreadsheet nobody trusts. Both fail the same way: the subscription needs internet and a card that keeps working, and the spreadsheet lets you sell fifty units of something you have thirty of.

InvoiceApp is a standalone Windows desktop app that keeps customers, vendors, products, stock, purchases, invoices, quotations, payments and returns in one local SQLite file. No server, no internet, no subscription. Default currency is Pakistani Rupee (PKR, "Rs"), changeable in Settings.

Documents that behave like documents

Invoices and quotations share a searchable, filterable list and an editor with product auto-fill that shows what's actually in stock. Per-line tax override, percentage or fixed discount, live totals, duplicate, print, PDF export — and one-click convert quotation → invoice, which is the step every shop does daily and most software makes you retype.

Seven PDF templates — Modern, Classic, Minimal, Bold, Corporate, Elegant, Compact — in A4 or Letter. Big company name and bill-to details, logo, itemised table with grid borders, totals, status badge, notes and terms, bank details, and signature boxes (prepared by / received by, with names). Long item lists paginate with the table header repeated, which sounds trivial until you've received page 3 of an invoice with no column labels.

Every document also gets a Show / hide sections & columns panel: turn off the status badge, due date, currency, logo, any table column, the discount, tax or paid lines, notes, terms, bank details, signatures or the grid. Defaults live in Settings → PDF layout. Different customers want different paperwork, and hardcoding one opinion means someone maintains a second template forever.

Numbering is prefix + counter + padding per document type, editable, with duplicates rejected.

Money, computed rather than typed

Payments support partial amounts and guard against overpayment. "Mark as paid" writes a real payment row instead of flipping a flag, so the payments log and the invoice can't disagree. There's a global payments log with CSV export.

Status is always computed — Unpaid, Partially Paid, Paid, Overdue. Nobody sets it by hand, so nobody forgets to.

Customer returns credit the invoice, dropping the balance, and can optionally put items back into stock. A return that fixes the money but not the shelf is how inventory drifts away from reality.

Inventory that says no

Products carry a cost price (what you paid) and a sale price, with margin shown to owners. Purchases from vendors add stock and update the cost price; returns to vendor remove it.

The rule that matters: invoices cannot sell more than is in stock. Fifty in stock means fifty is the maximum on an invoice. Owners can allow negative stock in Settings if their business genuinely works that way, but the default is the safe one. Editing an existing invoice frees its own stock first, so changing a line from 10 to 12 doesn't fail against stock the same invoice is holding.

On top: stock levels, low-stock alerts (global threshold or per product), stock adjustments, a full movement history, and best sellers by quantity, revenue and gross profit over a date range.

Roles, because not everyone should see the margin

First run creates the owner. Owners see everything — payments, purchases, costs, profit, vendors, settings, users. Employees work with invoices, quotations, customers, products (sale prices only) and can view stock — no payments, no costs, no deletes.

That split isn't paranoia, it's ordinary: the person at the counter needs to issue an invoice and should not be able to see what you paid the vendor, or quietly delete a document.

The owner dashboard shows outstanding, paid this month, overdue, open quotes, gross profit, stock value, low stock, purchases, best sellers and an activity feed. The employee dashboard shows counts only.

Nothing business-specific is hardcoded

Company profile and logo, currency, tax defaults, numbering, payment methods, default notes and terms, template and page size, bill-to heading, signature labels and names, PDF defaults, low-stock rules, live theme colours, backup and restore.

That list is the product. Software for small businesses usually dies on the one assumption the author never questioned — a currency symbol, a tax rate, a document label — and at that point it's someone else's tool you're fighting.

Why SQLite and why offline

One file holds everything. Backup is copying it. Restore is copying it back. There is no connection string, no migration server, no "the internet is down so we can't bill anyone."

And because it's a real database rather than a spreadsheet, the constraints above — stock limits, computed status, atomic payments — are actually enforced instead of being a convention everyone violates when it's busy.

Run from source

python -m pip install -r requirements.txt

Source: github.com/abdulmanan69/InvoiceApp. If your business needs something shaped like this — or the web version of it — get in touch.