Moolah Diaries: Vibe Coding a New Moolah

I got Claude to crunch the numbers on the moolah-native project — eight days of vibe coding a SwiftUI replacement for my long-running personal finance tracker, with zero Swift experience. The stats are interesting but they don’t really capture what the experience has been like, so here’s the human version.

Skipping the Learning Curve

Using AI to just skip the initial learning curve of a new language and platform has been really freeing. I don’t know Swift. I don’t know SwiftUI. Normally I’d spend a ton of time working out the basic setup and finding what patterns/libraries to use before I could do anything useful and that’s often enough to kill the motivation entirely. Instead I was working on actual domain problems from day one — straight to the interesting part. The learning curve didn’t go away, I just got to avoid it. Will this come back to bite me? Quite possibly.

Brainstorming with a Pretty Smart Duck

The brainstorming has been the standout. Claude Code has a brainstorming skill that walks you through refining designs interactively, and it’s been great. It found data sources for exchange rates, stock prices, and crypto prices that I’d missed even after searching pretty thoroughly myself. That opened up features I’d been uncertain about.

But the bigger win was at the design level. I’d previously looked at adding multi-currency support and even wrote a lot of the code but never really felt the design hit the complexity/benefit trade off. Working through the brainstorming process came up with a multi-leg transaction model that handles multicurrency much more cleanly and simplifies complexity around the existing transfer support. It’s rubber ducking, but with a duck reasonably smart duck (that has opinions and can pull up documentation you didn’t know existed).

The Cost Problem

AI usage limits are incredibly annoying. A Claude Pro plan is basically useless for anything beyond toy code — you’ll hit limits within an hour of real work. Gemini’s free tier is surprisingly capable for casual use, but if you want to actually sustain any kind of productivity you wind up needing Claude’s Max 20x plan and that’s a lot of money for a side project which may be dormant for long periods. For a business the cost is a no-brainer - it can make expensive engineers way more productive so pays for itself. For pesonal use when you have a family and look at costs in AUD, not so much.

The Bugs

Oh my god, the bugs. The analysis post puts the fix rate at 31% compared to 2.6% for the hand-written server. That tracks and maybe understates it. I’m pretty damn impressed with the low bug rate for moolah-server though given its a side project and I always felt like I was cutting corners and not writing tests that I should have.

Today was the worst day yet. At some point recently, AI had split iCloud sync profiles into separate CloudKit zones but they were actually still in a single zone, overlapping with each other. We’d talked about that and it was super confident it would work even when pressed on it and told to do deep research. Fixing that required migrating to a lower-level sync API (CKSyncEngine), which then triggered a cascade of stability problems and has taken pretty much the whole day to fix.

AI has the same instinct as a lot of engineers (including plenty of senior ones): when something breaks, keep throwing bandaids at the symptoms. Track more state. Add another deduplication pass. Cache another field. Each fix is locally reasonable but the complexity just ratchets up. I wound up having to step in and push it to throw away all the state tracking and just model the problem better so it automatically did the right thing. Less code, fewer bugs, simpler to reason about. But AI won’t get there on its own — it optimises for making the current test pass, not for finding a design where the test wouldn’t have failed in the first place.

Shipping is Still Hard

I’ve started entering transactions through the SwiftUI app but I’m still running the original moolah-server as the backend because I don’t trust the iCloud sync layer. Today is a pretty good example of why.

There’s also a subtler problem: vibe coding makes it very tempting to just keep churning out features because it’s fun to watch AI produce things. But every new feature is more unvalidated code, and that works against ever actually shipping. At some point you have to stop adding and start using. But I have nearly 15 years of historic data at risk and detecting subtle corruption or a few messed up transactions can be really hard.

It’s Fun Though

Coding was my hobby before it became my job. I still enjoy the job but it’s serious work with serious consequences. Vibe coding has brought back some of the fun of just playing with technology for its own sake — partly the quick results, but also just experimenting with a powerful new tool and learning how to get the most out of it.

The code quality concerns are real, the costs are high, and the bugs are maddening. But I built a functional multi-platform finance app in eight days with no platform experience, and I had a good time doing it.