Spec Driven Development With LLMs

There is a pattern that almost every engineer who has worked seriously with LLMs eventually discovers, usually after a few frustrating experiences: the quality of what you get out is determined almost entirely by the quality of what you put in. This is not a new observation. Every tool reflects the clarity of the instruction given to it. But with LLMs the relationship is more direct and more consequential than most engineers initially expect, because the model is capable enough to produce something plausible regardless of how good your input is. A vague prompt produces confident, coherent, and subtly wrong output. A precise prompt produces something you can actually use. The difference between those two outcomes is the spec. Spec-driven development is not a new concept either. Writing a clear specification before implementation has been good engineering practice for as long as engineering has existed. What is new is the leverage. When a well-written spec is the input to an LLM, the imp