// Creates specs before coding. Use when starting a new project, feature, or significant change and no specification exists yet. Use when requirements are unclear, ambiguous, or only exist as a vague idea.
| name | spec-driven-development |
| description | Creates specs before coding. Use when starting a new project, feature, or significant change and no specification exists yet. Use when requirements are unclear, ambiguous, or only exist as a vague idea. |
Write a structured specification before writing any code. The spec is the shared source of truth between you and the human engineer — it defines what we're building, why, and how we'll know it's done. Code without a spec is guessing.
When NOT to use: Single-line fixes, typo corrections, or changes where requirements are unambiguous and self-contained.
Spec-driven development has four phases. Do not advance to the next phase until the current one is validated.
SPECIFY ──→ PLAN ──→ TASKS ──→ IMPLEMENT
│ │ │ │
▼ ▼ ▼ ▼
Human Human Human Human
reviews reviews reviews reviews
Start with a high-level vision. Ask the human clarifying questions until requirements are concrete.
Surface assumptions immediately. Before writing any spec content, list what you're assuming:
ASSUMPTIONS I'M MAKING:
1. This is a web application (not native mobile)
2. Authentication uses session-based cookies (not JWT)
3. The database is PostgreSQL (based on existing Prisma schema)
4. We're targeting modern browsers only (no IE11)
→ Correct me now or I'll proceed with these.
Don't silently fill in ambiguous requirements. The spec's entire purpose is to surface misunderstandings before code gets written — assumptions are the most dangerous form of misunderstanding.
Write a spec document covering these six core areas:
Objective — What are we building and why? Who is the user? What does success look like?
Commands — Full executable commands with flags, not just tool names.
Build: npm run build
Test: npm test -- --coverage
Lint: npm run lint --fix
Dev: npm run dev
Project Structure — Where source code lives, where tests go, where docs belong.
src/ → Application source code
src/components → React components
src/lib → Shared utilities
tests/ → Unit and integration tests
e2e/ → End-to-end tests
docs/ → Documentation
Code Style — One real code snippet showing your style beats three paragraphs describing it. Include naming conventions, formatting rules, and examples of good output.
Testing Strategy — What framework, where tests live, coverage expectations, which test levels for which concerns.
Boundaries — Three-tier system:
Spec template:
# Spec: [Project/Feature Name]
## Objective
[What we're building and why. User stories or acceptance criteria.]
## Tech Stack
[Framework, language, key dependencies with versions]
## Commands
[Build, test, lint, dev — full commands]
## Project Structure
[Directory layout with descriptions]
## Code Style
[Example snippet + key conventions]
## Testing Strategy
[Framework, test locations, coverage requirements, test levels]
## Boundaries
- Always: [...]
- Ask first: [...]
- Never: [...]
## Success Criteria
[How we'll know this is done — specific, testable conditions]
## Open Questions
[Anything unresolved that needs human input]
Reframe instructions as success criteria. When receiving vague requirements, translate them into concrete conditions:
REQUIREMENT: "Make the dashboard faster"
REFRAMED SUCCESS CRITERIA:
- Dashboard LCP < 2.5s on 4G connection
- Initial data load completes in < 500ms
- No layout shift during load (CLS < 0.1)
→ Are these the right targets?
This lets you loop, retry, and problem-solve toward a clear goal rather than guessing what "faster" means.
With the validated spec, generate a technical implementation plan:
The plan should be reviewable: the human should be able to read it and say "yes, that's the right approach" or "no, change X."
Break the plan into discrete, implementable tasks:
Task template:
- [ ] Task: [Description]
- Acceptance: [What must be true when done]
- Verify: [How to confirm — test command, build, manual check]
- Files: [Which files will be touched]
Execute tasks one at a time following skills/incremental-implementation/SKILL.md (incremental-implementation) and skills/test-driven-development/SKILL.md (test-driven-development). Use skills/context-engineering/SKILL.md (context-engineering) to load the right spec sections and source files at each step rather than flooding the agent with the entire spec.
The spec is a living document, not a one-time artifact:
| Rationalization | Reality |
|---|---|
| "This is simple, I don't need a spec" | Simple tasks don't need long specs, but they still need acceptance criteria. A two-line spec is fine. |
| "I'll write the spec after I code it" | That's documentation, not specification. The spec's value is in forcing clarity before code. |
| "The spec will slow us down" | A 15-minute spec prevents hours of rework. Waterfall in 15 minutes beats debugging in 15 hours. |
| "Requirements will change anyway" | That's why the spec is a living document. An outdated spec is still better than no spec. |
| "The user knows what they want" | Even clear requests have implicit assumptions. The spec surfaces those assumptions. |
Before proceeding to implementation, confirm:
Extracts what the user actually wants instead of what they think they should want. Achieves this through one-question-at-a-time interview until ~95% confidence about the underlying intent. Use when an ask is underspecified ("build me X" without "for whom" or "why now"), when the user explicitly invokes ("interview me", "grill me", "are we sure?", "stress-test my thinking"), or when you catch yourself silently filling in ambiguous requirements before any plan, spec, or code exists.
Discovers and invokes agent skills. Use when starting a session or when you need to discover which skill applies to the current task. This is the meta-skill that governs how all other skills are discovered and invoked.
Tests in real browsers via Chrome DevTools MCP. Use when building or debugging anything that runs in a browser. Use when you need to inspect the DOM, capture console errors, analyze network requests, profile performance, or verify visual output with real runtime data. Requires the chrome-devtools MCP server to be configured.
Refines raw ideas into sharp, actionable concepts through structured divergent and convergent thinking. Use when an idea is still vague, when you need to stress-test assumptions before committing to a plan, or when you want to expand options before converging on one. Triggers on "ideate", "refine this idea", or "stress-test my plan".
Subjects every non-trivial decision to a fresh-context adversarial review before it stands. Use when correctness matters more than speed, when working in unfamiliar code, when stakes are high (production, security-sensitive logic, irreversible operations), or any time a confident output would be cheaper to verify now than to debug later.
Delivers changes incrementally. Use when implementing any feature or change that touches more than one file. Use when you're about to write a large amount of code at once, or when a task feels too big to land in one step.