The Design Doc Was Wrong. AI Trusted It Anyway. (opens in new tab)

I was building a new module for a side project, and the design document looked thorough. Claude had written it, I had reviewed it, and everything seemed reasonable. One section described how to calculate a derived value from two stored fields — both multiplied by 100 to preserve two decimal places — and gave the formula: Result = fieldA × 100 × fieldB × 100 / 10000 The logic made sense on the surface. Both fields carried 100x precision, so the divisor cancels them out. DeepSeek implemented it...