We ditched the backend to build a "Sovereign" B2B FinTech tool (And dropped our server costs to $0)

Hey Indie Hackers! 👋

When building B2B SaaS—especially in FinTech or capital planning—the biggest hurdle isn't just the math, it's trust. CFOs and enterprise leaders hate sending sensitive financial data to third-party API servers.

To solve this, my team bootstrapped and shipped the SEOSiri CapEx Engine (https://capex.seosiri.com). Instead of building a traditional backend API, we built a 100% "Sovereign, Browser-Based" calculator.

Here are 3 lessons from building a purely client-side B2B app:

1. "Sovereign Data" is a Massive Selling Point
   Because we process complex calculations (like NPV and IRR) entirely in the user's browser using optimized JavaScript, the data never leaves their local machine. We can honestly tell enterprise users: "We literally cannot see your financial data." In B2B, privacy is a killer feature.

2. Zero Backend = Zero Compute Costs
   By eliminating the backend data-processing layer, our infrastructure costs dropped to basically zero. The app is just a static payload deployed at the edge. Once the HTML/JS loads, the user has a full, audit-grade financial calculator. Bootstrapping is much easier when your server costs don't scale with your users' heavy calculations.

3. Speed is the Best UI
   Legacy ERP tools take seconds to load heavy database queries. Because our engine runs purely on the client side, there is zero network handshake or API latency. The numbers update in sub-milliseconds as the user adjusts the sliders.

Are you building local-first or purely client-side tools? How are you handling complex business logic without a heavy backend? Let’s talk in the comments! 👇