Why I stripped Firebase and built an offline-first budget vault on Flutter & SQLite?

I am a Banking Professional, and like many developers and finance enthusiasts, I hit a breaking point with modern personal finance software.

Almost every mainstream budgeting app (YNAB, Monarch, Copilot) operates on the exact same playbook:

1. Mandatory cloud account synchronization.
2. Third-party bank scraping integrations (Plaid/Yodlee).
3. Recurring, aggressive annual subscriptions ($100+/year).
4. Invasive corporate telemetry tracking your spending behavior.

I wanted a personal financial command center with absolute data sovereignty. That led to engineering MyneWallet around a strict architectural constraint: the network is disabled by default.

Here is why we tore out cloud infrastructure, stripped Firebase, and built a local-first financial engine on Flutter and SQLite.

The Problem with the Default "Firebase Stack" for Finance

When bootstrapping a mobile app in Flutter, the default advice is always: Throw Firebase Auth, Firestore, and Firebase Analytics at it.

For a privacy-first financial vault, that default stack is a liability:

- Third-Party Telemetry & Surveillance: Even if you don't actively log sensitive transactions, including tracking SDKs links device IDs, IP addresses, and behavioral metrics back to corporate ad networks.
- Binary Bloat & Cold Start: Stripping Firebase SDKs immediately trimmed megabytes off the release APK and reduced cold-start initialization to under 300ms.
- The "Always-Online" Trap: When your app relies on cloud sync, an offline subway ride or poor reception turns a 2-second expense entry into a spinning loader.

We decided that a financial breach cannot expose our users' data if we don't have servers to breach in the first place.

Key Architectural Decisions

- On-Device SQLite Sandbox: The entire financial ledger resides in an encrypted SQLite database stored securely inside the Android OS application sandbox. No external servers, no account registration screens, and zero remote data storage.
- Strict Integer Mathematics: In fintech, 0.1 + 0.2 != 0.3 is an unacceptable failure mode. All currency calculations in MyneWallet are processed and stored as integer minor units (cents). Every ledger balance mutation runs in atomic database transactions, preventing rounding drift across multi-year projections.
- Zero Telemetry SDKs: There are no advertising SDKs, product trackers, or crash-reporting pipelines sending pings home. If a user turns on Airplane Mode, 100% of the app—including 60fps hardware-accelerated analytics—functions without friction.
- Client-Side Cryptographic Backups: Cloud backup is strictly opt-in to the user's personal Google Drive. The archive is encrypted locally on-device using AES-256 with randomized initialization vectors (IV) before any network socket is opened. We never hold the keys.
- True Zero-Based Budgeting (ZBB) Engine: Built strictly on the envelope methodology: every dollar gets a destination. We engineered a real-time Auto-Assign engine and an honest "Safe to Spend" metric that isolates liquid cash from money already committed to future bills or emergency reserves.

Why We Killed the Subscription Model

Modern software suffers from massive subscription fatigue. Paying monthly rent just to track what you already earned makes no financial sense.

The core tracking and budgeting engine in MyneWallet is free forever with zero ads. For power users wanting multi-year analytics, spending heatmaps, and Sankey cash-flow diagrams, it’s a single One-Time Lifetime Unlock. Buy it once, own it for life.

- Google Play: https://play.google.com/store/apps/details?id=com.thebrinklabs.mynewallet.expensetracker
- Web & Architecture Manifesto: https://thebrinklabs.com/mynewallet/

We also deployed 6 client-side, zero-tracking financial instruments on the web (Zero-Based Budget Allocator, Subscription Bleed Audit, Debt Payoff, Net Worth Calculator):
https://thebrinklabs.com/tools/

Over to You

I would love feedback from the community on our local-first constraints:

• How do you approach offline-first database synchronization without compromising privacy?
• Have you ditched third-party telemetry in your own apps?

I’ll be in the comments answering questions and discussing the Flutter/SQLite architecture!

Comments

[SynDiary]

For personal data, I think local-first becomes especially important when the value of the app grows over years. The difficult part is making users understand that benefit before they’ve accumulated years of data.

[Asiv]

Spot on. Long-term sovereignty is an abstract promise on Day 1; lock-in only hurts when years of data are already held hostage.

That’s why a local-first app has to win on immediate, tactile utility first: zero onboarding friction, no sign-up screens, and instant, sub-second logging.

The raw speed hooks them today; the local SQLite architecture protects them five years down the road.

Judging by your handle, I imagine you face this exact challenge in journaling—how do you approach that day-one perception hurdle?

[SynDiary]

Exactly. I’m a co-founder of SynDiary, although it’s more than journaling. We’re building it as a private personal data hub.

We face the same challenge: long-term ownership and privacy matter, but they are rarely enough to make someone open a new app today. Our most immediate starting point is calendar synchronisation, because people already have data there and can see part of their timeline without beginning from an empty screen. They can then add structured entries, voice recordings with transcription, or import their Facebook and Instagram archives.

We’re still learning which of those creates the real first “aha” moment and makes someone return. For your budget vault, what seems to hook people first: the speed of logging something, or immediately seeing something useful from the data?

[Asiv]

Starting from a blank screen is the silent killer of personal tracking apps—your calendar sync strategy makes complete sense.

For us, it is a two-part sequence:

The Instant "Aha" (Eliminating the Blank Slate): We built a full CSV import engine. The moment a user drops in an existing bank or ledger export, the local SQLite database populates and the analytics engine (spending heatmaps, Sankey cash flows) lights up instantly. They get immediate visual gratification without manual entry.

The Retention Hook (Daily Habit): Once the baseline exists, friction-free speed takes over. The 3-second quick log at the checkout counter is what keeps them from abandoning the habit.

Visualizing historical data gets them through the door; sub-second capture keeps them in the room. By the way, Good Luck for your SynDiary!