Guide
Spec-Driven Development with AI Coding Agents
Last updated: October 27, 2026
Spec-driven development means you write down what the software must do before anyone builds it. The spec is the source of truth. Code, tests and reviews all point back to it.
The idea is old. It matters again because AI coding agents now write a large share of the code. An agent is fast, but it does exactly what it was told. If nobody told it the edge cases, it guesses.
Why AI agents need a spec
Give a coding agent a one-line prompt and it fills every gap with its own assumptions. Some of those assumptions are wrong, and you find out in review, or later in production.
A spec closes those gaps up front. It says who the feature is for, what done looks like, and what the agent must not touch. The agent then has less to guess, and the reviewer has something to check the result against.
What a good spec contains
- Why. The problem and who has it.
- What. The behaviour, written as acceptance criteria you can test.
- How. Constraints on the design, such as the API shape or a latency budget.
- Guardrails. What must not change, and what needs a human to approve.
Open questions belong in the spec too. A question written down is cheaper than a wrong answer built into the code.
Spec-driven development vs. vibe coding
Vibe coding is prompting an agent until the output looks right. It works for a weekend prototype. It breaks down on a team, because nobody can say what the code was supposed to do, only what it does now.
With a spec, the agent still does the typing. The difference is that a person approved the intent first, and every change can be traced back to it.
How nTra runs spec-driven development
nTra is a spec-driven product engineering platform: every task your AI coding agents build traces back to a requirement your business signed off. It is built around this loop. You start with a discovery chat. nTra asks the questions a senior product manager would ask and writes the brief as you answer, with a depth score that shows what is still thin.
Nothing is planned or built until you approve the brief. After that, nTra turns it into documents, screens and a sized task list. Each task then runs through your own coding agent, on your computer or in our cloud, and ends as a pull request your team reviews.
See the full loop on how nTra works, or compare plans.