## Definition **Spec-Driven Development (SDD)** is a methodology in which a written specification is treated as the primary, executable artifact of a software project. Code is a regenerable output produced from the spec by humans, AI agents, or both. SDD emerged in 2025 as the response to "vibe coding" — agent output that produces plausible code drifting from intent. ## Central Thesis > The spec is the program. The code is its current implementation. When the spec changes, the code is wrong until proven otherwise — and the spec itself tells you how to prove it. ## Why Now Agents changed the economics. A spec is no longer a hand-off artifact between humans; it is the **prompt template** that runs every time an agent picks up the work. Vague specs produce vague code; executable specs produce code that *fails noisily when wrong*. ## Observed Impact Early-adopter reports (GitHub, AWS) cite ~3–10× higher first-pass success rate from AI agents on non-trivial tasks under SDD versus ad-hoc prompting. ## Tool Landscape (2026) GitHub Spec Kit, AWS Kiro, Cursor, [[OpenSpec]], [[BMAD Method]], Tessl, Google Antigravity, Claude Code's skills + agents implementation. See [[OpenSpec and the SDD Tools Map 2026]]. ## Related - [[SDD Spectrum]] - [[Executable Acceptance Criterion]] - [[Gherkin Scenario]] - [[Spec-as-Prompt Pattern]] - [[OpenSpec]] - [[BMAD Method]]