The original title is about building an invoice generator with no backend as a single HTML file. Let me rewrite this following the rules.

Short summary

Billfold is a privacy-first invoice generator that runs entirely in the browser as a single HTML file — no backend, no account, no framework. Invoice data is encoded into URL hash fragments for sharing, and a paid tier uses ECDSA-signed keys verified client-side via Web Crypto API. The author also published an npm helper for building pre-filled invoice links programmatically.

• •Single-file HTML invoice app with zero network requests — data stays in localStorage
• •Sharing works by encoding full invoice state into URL hash fragments, never touching a server
• •Paid tier uses client-side ECDSA key verification; no activation call needed

Generated with AI, which can make mistakes.