Spec-Driven Development
The methodology for building AI-assisted software that actually ships. Define your specs before writing code. Eliminate hallucinations. Ship with confidence.
What is Spec-Driven Development?
Spec-Driven Development (SDD) is a software development methodology where you define complete specifications—API contracts, database schemas, architecture diagrams, and acceptance criteria—before writing implementation code.
In the age of AI coding assistants, SDD isn't just a best practice—it's a survival strategy. LLMs need constraints to produce reliable output. Without specs, they hallucinate. With specs, they execute.
The Core Principle
“Specs are not documentation. Specs are constraints.”
SDD vs Other Methodologies
Specs → Code → Tests
Define all constraints upfront, then build.
Tests → Code → Refactor
Tests drive development, but no system-wide constraints.
Behavior → Tests → Code
User-focused, but often lacks technical contracts.
Prompt → Hope → Debug
No constraints. Maximum hallucinations.
Why Vibe Coding Fails at Scale
The honeymoon phase is real. The hangover is worse.
Fast Start, Slow Finish
You can build a prototype in hours. But the last 20% takes 80% of the time because you're debugging invented APIs and phantom dependencies.
Scope Drift
No spec means no boundaries. AI keeps adding “helpful” features you never asked for. Your MVP becomes a monster.
Integration Hell
Multiple AI sessions create incompatible components. Without a shared contract, nothing fits together.
The SDD Stack
Five layers of constraints that eliminate hallucinations.
Product Requirements (PRD)
Goals, non-goals, user personas, and feature scope. This is the “what” and “why” before anyone touches code.
Generate PRDData Model (Schema)
Entity relationships, field types, constraints, and indexes. The single source of truth for your data structure.
View Schema TemplateAPI Contracts (OpenAPI)
Every endpoint, request body, response shape, and error code—defined before implementation. No invented methods.
View API TemplateArchitecture
Component structure, data flow, integration points, and deployment topology. The blueprint that prevents spaghetti.
Browse Architecture TemplatesAI Rules (.cursorrules)
Enforce your stack, coding patterns, and conventions. Lock the AI to your constraints so it can't drift.
Generate Cursor RulesStart Building with SDD
Run a free Spec Readiness Score to see which layers of the SDD stack you're missing.
Start here
Spec-driven workflow: diagnose → generate → export → validate
Use the tools below to turn SDD into a repeatable shipping system.