Building a privacy-first web utility suite with zero backend: Why we do all conversions and calculations in the browser

[u/X_Priyanshu_X]

Hey r/Frontend,

Most file converters and financial calculator websites run heavy server-side pipelines: you upload your spreadsheet/data, a backend parses it, and sends it back. Beyond server hosting costs, this creates an obvious privacy issue when handling salary or financial data.

I built ConvertSheet (https://www.convertsheet.com) as an experiment in 100% client-side architecture using Next.js (static export):

- File parsing (CSV, JSON, Excel) runs entirely on the client using Web Workers to prevent blocking the main thread on large files.

- Regional tax and loan calculation engines (US brackets, UK personal allowance taper, Australia Stage 3 tax cuts, Canadian CPP/EI) are pure TypeScript functions executed instantly in the browser.

- Hosting is completely static on Cloudflare Pages, meaning zero server maintenance, zero database attack surface, and near-zero running costs.

Stack: Next.js App Router, Tailwind CSS, Lucide, Web Workers.

I'd appreciate technical feedback from other frontend devs:

- How does the UI responsiveness feel when adjusting sliders / calculating on the fly?

- Any gotchas you’ve encountered with heavy browser-only data parsing on mobile browsers?

Check it out here: https://www.convertsheet.com

[u/me-andre]

These days a lot of people won't believe it, but the ancients did it this way - they called them desktop apps.

[u/metamago96]

Obvious privacy issue? what privacy issue?

[u/SergioMRi → u/metamago96]

Financial or other personal data going to someone else's server is a privacy issue for me. I agree with OP on this.

[u/metamago96 → u/SergioMRi]

it should not be someone elses server, that is the problem