Spec Driven Development

The specification stops being a supporting document and becomes the source of truth: you describe behaviour, constraints and acceptance criteria, and the agent generates code against that description. The name is old and comes from the same family as documentation-driven development and model-driven engineering, but what it means changed once the reader of the specification stopped being human.

The difference is in who reads it. A design document from the 2000s was opened by a team months later, and whoever read it was suspicious of anything that looked out of date. An agent reads the same stale specification and executes it with confidence, which turns an old document from an annoyance into a defect.

Every tool implements the method with a different set of stages, and they are not compatible with each other. What shows up in all of them, according to a 2026 comparison of seven frameworks, is three things: acceptance criteria, test scenarios and context alignment.