Billing & GST Filing System -- 2

I need a straightforward system that lets me record every sale and purchase, then automatically calculates the correct CGST, SGST or IGST and prepares all the summaries required for my periodic GST returns. The key outcome is a one-click export of GSTR-1 and GSTR-3B (JSON or Excel) that I can upload directly to the government portal, along with a clear dashboard showing my current liabilities and input credits.

Although my immediate priority is GST calculation and filing, it would be helpful if the architecture leaves room for future additions such as invoice generation or even inventory tracking, so please keep the codebase modular.

Deliverables
• A working desktop or web application (Windows-friendly or browser-based)
• Accurate GST computation engine with HSN/SAC support
• Return-ready files for GSTR-1 and GSTR-3B
• Basic user guide and short onboarding session
• Source code and documentation sufficient for future feature expansion

Acceptance criteria
1. I can input at least 1000 transactions without noticeable lag.
2. Tax values match the government portal’s validation tool.
3. Exported JSON uploads without errors.

Feel free to choose the tech stack you’re comfortable with—just make sure it stays lightweight, secure, and easy for a non-technical user to operate.