Notes on Spec-Driven Development

For most of my career, the code was the spec. If you wanted to know what a service actually did, you read the service — the README was a suggestion, and the ticket description was ancient history by the time the PR landed.

Spec-driven development flips that assumption, and working within an AI Enabler initiative has forced me to take it seriously rather than treat it as process theater.

The shift

When an AI coding agent is doing a meaningful share of the implementation, a vague spec doesn’t just slow a human down — it sends the agent confidently in the wrong direction, fast. That changes the incentive: writing the spec well becomes the highest-leverage part of the task, not a formality before the “real work” starts.

In practice, that means:

• Defining the contract (inputs, outputs, edge cases) before touching a controller or service class
• Writing acceptance criteria specific enough that both a human reviewer and an agent could verify them
• Treating the spec as a living artifact that gets updated when reality diverges from the plan, not archived the moment coding starts

Where it earns its keep

This pays off most in microservice work — exactly the kind of environment I work in day to day. A clear spec for a new endpoint or a refactored service boundary means less back-and-forth in review, and it means an AI-assisted first pass is actually usable instead of something you have to unwind and redo.

It doesn’t replace engineering judgment. It front-loads it, so the judgment happens once, deliberately, instead of getting relitigated in every PR comment.