LLM agents write code at astonishing speed. They also forget at astonishing speed. A conversation may contain important decisions, yet those decisions disappear when the session, model, maintainer, or available context changes.

That is where Spec-Driven Development (SDD) comes in. The idea is simple: before asking for code, write down what we want to build, why, which boundaries it must respect, and how we will know it works. The specification stops being an ephemeral document and becomes a working contract that both the team and its agents can read.