---
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.
---

# Spec-Driven Development

## Policy Capsule

- Follow the gated workflow: **Specify → Plan → Tasks → Implement**. Never advance until the human has reviewed and approved the current phase.
- Surface assumptions explicitly **before** writing spec content: list them as "ASSUMPTIONS I'M MAKING" and ask the human to correct them. Never silently fill in ambiguous requirements.
- Reframe vague requirements (e.g. "make it faster") as specific, testable success criteria with numeric targets before accepting them as scope.
- Phase 1 specs MUST cover all six core areas: **Objective, Commands, Project Structure, Code Style, Testing Strategy, Boundaries**.
- The Boundaries section is three-tier and mandatory: **Always do** / **Ask first** / **Never do**. Database schema changes, dependency additions, and CI changes default to "Ask first".
- Provide commands as full executable strings (with flags), not just tool names; provide code style as a real snippet plus key conventions, not prose-only descriptions.
- Phase 3 tasks each have explicit acceptance criteria, a verification step (test/build/manual), declared file scope (≤ ~5 files), and dependency-ordered sequencing.
- Treat the spec as a **living document** — update it first when decisions or scope change, commit it to version control, and link the relevant section from each PR.
- Do not start implementation until the spec has been reviewed, success criteria are specific and testable, boundaries are defined, and the spec lives in the repo.

## Overview

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 to Use

- Starting a new project or feature
- Requirements are ambiguous or incomplete
- The change touches multiple files or modules
- You're about to make an architectural decision
- The task would take more than 30 minutes to implement

**When NOT to use:** Single-line fixes, typo corrections, or changes where
requirements are unambiguous and self-contained.

## The Gated Workflow

Spec-driven development has four phases. Do not advance to the next phase until
the current one is validated.

```text
SPECIFY ──→ PLAN ──→ TASKS ──→ IMPLEMENT
   │          │        │          │
   ▼          ▼        ▼          ▼
 Human      Human    Human      Human
 reviews    reviews  reviews    reviews
```

### Phase 1: Specify

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:

```text
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:**

1. **Objective** — What are we building and why? Who is the user? What does
   success look like?

2. **Commands** — Full executable commands with flags, not just tool names.

   ```text
   Build: npm run build
   Test: npm test -- --coverage
   Lint: npm run lint --fix
   Dev: npm run dev
   ```

3. **Project Structure** — Where source code lives, where tests go, where docs
   belong.

   ```text
   src/           → Application source code
   src/components → React components
   src/lib        → Shared utilities
   tests/         → Unit and integration tests
   e2e/           → End-to-end tests
   docs/          → Documentation
   ```

4. **Code Style** — One real code snippet showing your style beats three
   paragraphs describing it. Include naming conventions, formatting rules, and
   examples of good output.

5. **Testing Strategy** — What framework, where tests live, coverage
   expectations, which test levels for which concerns.

6. **Boundaries** — Three-tier system:
   - **Always do:** Run tests before commits, follow naming conventions,
     validate inputs
   - **Ask first:** Database schema changes, adding dependencies, changing CI
     config
   - **Never do:** Commit secrets, edit vendor directories, remove failing tests
     without approval

**Spec template:**

```markdown
# 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:

```text
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.

### Phase 2: Plan

With the validated spec, generate a technical implementation plan:

1. Identify the major components and their dependencies
2. Determine the implementation order (what must be built first)
3. Note risks and mitigation strategies
4. Identify what can be built in parallel vs. what must be sequential
5. Define verification checkpoints between phases

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."

### Phase 3: Tasks

Break the plan into discrete, implementable tasks:

- Each task should be completable in a single focused session
- Each task has explicit acceptance criteria
- Each task includes a verification step (test, build, manual check)
- Tasks are ordered by dependency, not by perceived importance
- No task should require changing more than ~5 files

**Task template:**

```markdown
- [ ] Task: [Description]
  - Acceptance: [What must be true when done]
  - Verify: [How to confirm — test command, build, manual check]
  - Files: [Which files will be touched]
```

### Phase 4: Implement

Execute tasks one at a time following `incremental-implementation` and
`test-driven-development` skills. Use `context-engineering` to load the right
spec sections and source files at each step rather than flooding the agent with
the entire spec.

## Keeping the Spec Alive

The spec is a living document, not a one-time artifact:

- **Update when decisions change** — If you discover the data model needs to
  change, update the spec first, then implement.
- **Update when scope changes** — Features added or cut should be reflected in
  the spec.
- **Commit the spec** — The spec belongs in version control alongside the code.
- **Reference the spec in PRs** — Link back to the spec section that each PR
  implements.

## Common Rationalizations

| 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.                     |

## Red Flags

- Starting to write code without any written requirements
- Asking "should I just start building?" before clarifying what "done" means
- Implementing features not mentioned in any spec or task list
- Making architectural decisions without documenting them
- Skipping the spec because "it's obvious what to build"

## Verification

Before proceeding to implementation, confirm:

- [ ] The spec covers all six core areas
- [ ] The human has reviewed and approved the spec
- [ ] Success criteria are specific and testable
- [ ] Boundaries (Always/Ask First/Never) are defined
- [ ] The spec is saved to a file in the repository
