What is spec-driven development?
Spec-driven development (SDD) is a way of building software where you write a precise specification first, then implement against it. The spec describes what to build, the constraints, and how you will know it works. It has gained new attention because AI coding agents follow a good spec far better than a vague chat prompt. The spec, not the conversation, becomes the source of truth.
In plain words
It is the difference between telling a builder "make me a nice kitchen" and handing them a labelled floor plan with measurements. The plan removes guesswork. Both a human and an AI agent build the right thing the first time, because the decisions were made before anyone picked up a tool.
When to use it
- Anything non-trivial. For a one-line fix, a spec is overkill. For a feature with edge cases and tradeoffs, writing it down pays off fast.
- When AI agents do the coding. Agents lose the thread on long, fuzzy tasks. A structured spec keeps them aligned with what you actually wanted.
- When several people are involved. A spec is a shared agreement. It catches misunderstandings before they become rework.
- When you want reviewable decisions. The spec records why you chose an approach, which helps the next person who touches the code.
Common pitfalls
- Over-specifying. A spec that dictates every line becomes a second codebase to maintain. Capture intent and constraints, not implementation trivia.
- Writing it once and forgetting it. If the spec drifts from reality, people stop trusting it. Update it when decisions change.
- Treating it as a contract to hide behind. A spec guides the work; it does not replace talking to each other when something turns out to be wrong.
Related articles:
- What is a definition of done? - The shared checklist that pairs well with a spec.
- What is prompt engineering? - Writing clear instructions, the foundation a spec builds on.
- What is agentic AI? - The AI agents that benefit most from a clear spec.
Want to stay one step ahead?
Don't miss our best insights. No spam, just practical analyses, invitations to exclusive events, and podcast summaries delivered straight to your inbox.