Stop building fintech with databases. Why I went local-first for Pocket Portfolio.
For the last decade, building a fintech app meant one architecture: a centralized PostgreSQL database, a backend in Node or Python, and an API that hoards user data.
As an engineer, I always found this disturbing. Why does a portfolio tracker need my trade history stored on AWS us-east-1? It does not. It stores it because the data is the product, not the software.
I wanted to build a tool for modern investors — those of us using Trade Republic, Trading 212, or Robinhood — who want insights without surveillance.
So I set a hard constraint:
Zero user data leaves the client.
That constraint became the foundation of Pocket Portfolio — a privacy-absolute, local-first financial application.
The Zero-Server Stack
We stripped everything back.
There is no backend database.
No user accounts.
No cloud sync.
- The Core: Next.js (static export). The entire app is JavaScript shipped to the browser.
- The Database: Browser storage (localStorage and IndexedDB). Your financial data lives on your device, not ours.
- The Parser: Web Workers processing CSV files entirely client-side.
No servers storing user data. No silent replication. No surveillance by default.
The Hardest Part: Client-Side Parsing
The hardest technical problem was not charts or performance.
It was standardizing messy, inconsistent CSV exports from more than 15 brokers — without sending a single byte to a server.
Each broker formats exports differently. Headers change. Dates vary by locale. Fees are embedded or omitted. Some files are technically valid CSVs but semantically broken.
So we built a robust, open-source parsing engine that runs entirely in the browser.
The flow looks like this:
- User drops a CSV file (for example, a 5MB Trade Republic export).
- The main thread hands the file to a Web Worker to avoid UI freezes.
- The worker identifies the broker schema and normalizes each row into a standard JSON format.
- Clean data is returned to the main thread and hydrated into application state.
All of this happens locally. No uploads. No APIs.
The Market Has Spoken
I was not sure if other developers cared about this level of privacy. I was wrong.
Within the first seven days of soft-launching the parser engine on npm, it crossed 5,800+ weekly downloads.
Developers are already integrating the local parser into their own pipelines.
The takeaway is simple:
You do not need to hoard user data to build valuable software.
Try It (and Break It)
Pocket Portfolio is live.
If you are an investor or a developer tired of the current fintech status quo, try it with your messiest CSV file and see how the local engine handles it.
We are also running a limited Founder’s Club for early supporters who believe in local-first software and want lifetime access to advanced features.
Keep building.
Keep it local.
