Spec-driven development
What is Spec-driven development?
A method where the specification, not the code, is the primary artefact. Developers write and refine a structured spec, and an AI coding agent generates code to match it. An open-source toolkit released in 2025 runs a Spec, Plan, Tasks, Implement flow. It is the fast-rising discipline for keeping AI-built software true to intent, instead of drifting prompt by prompt.
Why it matters
Building by prompt has a failure mode that only shows up over time. Each request nudges the code a little, the reasoning behind each nudge lives in a chat log nobody keeps, and after a few weeks no single artefact explains why the system does what it does. Putting the specification first fixes that by moving the source of truth out of the conversation and into a document you can version, review and hand to someone new. When the requirement changes you edit the spec and regenerate, rather than patching code and hoping the intent survives. The discipline it demands is real, since a vague spec produces vague software just as surely as a vague prompt did. The gain is that the thing you argue over and sign off is the thing that actually drives the build.
In practice
The spec lives in the same repository as the code, under review like any other change. A new requirement lands as an edit to the spec, discussed in a pull request, then the implementation is regenerated to match. Six months on, an engineer who never saw the original conversation can read the spec and know what the system is meant to do, and why.
