Rules-Based Investing for Developers: How I Automated My Investment Decisions

Last year, I merged a PR that cost me $4,200. Not at work — in my brokerage account. I'd been so deep in a sprint that I forgot to check on a position that had hit my mental stop-loss two weeks earlier. By the time I remembered, the damage was done. The irony hit me hard: I would never deploy code without automated tests, but I was managing my life savings with "I'll remember to check it later." That night, I started building a rules-based investment system using the same engineering principles I apply to software every day. And honestly, it's been one of the most impactful side projects I've ever done — not because it made me rich, but because it made me consistent. Developers Already Think Like Investors (They Just Don't Know It) Consider how similar these mindsets are: Software Engineering Investing Don't ship without tests Don't buy without due diligence Avoid premature optimization Avoid market timing Reduce technical debt Avoid excessive financial leverage Code review before merg