SwiftInvoice

The app layer behind SwiftInvoice: accounts, clients, invoices, public invoice links and plan limits, built as a WordPress plugin with its own REST API.

SwiftInvoice runs on a custom WordPress plugin that acts as the full application layer. It handles sign-up with email verification and throttled sign-in, then gives each account its own clients and invoices, stored in custom tables and served through a dedicated REST API.

Invoice totals are calculated on the server in minor units, so amounts stay exact. Each invoice gets a public link with view tracking, free and paid plans enforce their limits, and the plugin also outputs structured data and SEO files for the marketing site.