A conscice, self contained, unassuming little function that represents some out of the box thinking to vastly simplify a previously hard problem. Those 25 lines are backed by several months and 10+ pages of analysis establishing that their simple approach is at least as good as the obvious approach, which would have meant integrating several very complex dependencies. Never been prouder of a diff so small.

Close second, a system I designed and built 2.5 years ago, which faded into the background and plugged along. Business interest has renewed, and everything they’re now asking for fits neatly into the architecture. Really satisfying to see something hold up.