Invoice & Payslip Maker
A web app for automatically generating invoices and payslips from custom Word/Excel templates, with automated payment follow-up via email. Built with Next.js, TanStack Query, and Neon (Postgres).
InvoiceMaker & Payslip is a web application I built to handle invoicing and payroll administration — generating invoices and payslips without manually editing Word or Excel files each time. Instead of building a template generator from scratch, the app works directly with custom-designed Word (.docx) templates for invoices and Excel (.xlsx) templates for payslips, dynamically filling them with data and converting the output into ready-to-send PDFs.
One of the main technical challenges was producing PDFs that preserve the original formatting of the Word and Excel templates, rather than simply re-rendering the content as HTML. To solve this, I used docxtemplater to fill placeholders in the Word template, ExcelJS to populate cells in the Excel template, and LibreOffice headless to consistently convert both formats into PDF.
The app also includes an automated invoice follow-up feature: the system periodically checks for unpaid invoices that are approaching or past their due date, then sends reminder emails to the relevant clients without any manual intervention.
Key features:
Invoice generation from a Word template with client, item, and due-date data
Payslip generation from an Excel template with salary components, allowances, and deductions
Automated email follow-up for overdue invoices
Centralized history of all generated invoices and payslips
Final output exported as PDF