Agent Skills: Spec-Driven Development (SDD)

Spec-Driven Development (SDD)

Core Principle

1 Todo = 1 Commit = 1 Spec Update

Every task must:

1. Have a corresponding specification entry
2. Result in a focused commit
3. Update relevant documentation

Workflow

Phase 1: Specification

Before writing code, create or update the specification:

docs/
  PRD.md           # Product Requirements Document
  specs/
    feature-x.md   # Feature-specific specifications
  CHANGELOG.md     # All changes tracked here

Phase 2: Implementation

1. Read the relevant spec from docs/specs/
2. Create focused todo items (1 todo = 1 atomic change)
3. Implement following the spec exactly
4. Validate implementation matches spec

Phase 3: Documentation Sync

After each implementation:

1. Update CHANGELOG.md with the change
2. Update spec if implementation revealed necessary changes
3. Commit with message referencing the spec

File Structure

PRD.md Template

# Product Requirements Document

## Overview
[Brief description]

## Goals
- Goal 1
- Goal 2

## Features
### Feature A
- **Status**: [Planned | In Progress | Done]
- **Spec**: [Link to detailed spec]
- **Priority**: [High | Medium | Low]

## Non-Goals
[What this project will NOT do]

Feature Spec Template

See references/spec-template.md for the full template.

CHANGELOG.md Format

# Changelog

## [Unreleased]

### Added
- Feature description (spec: feature-x.md)

### Changed
- Change description

### Fixed
- Fix description

Commands

Create New Spec

When user says "create spec for X":

1. Generate spec from template
2. Save to docs/specs/X.md
3. Add entry to PRD.md
4. Create initial CHANGELOG entry

Implement from Spec

When user says "implement X" or "build X":

1. Read docs/specs/X.md
2. Break into atomic todos
3. For each todo:
   • Implement the change
   • Validate against spec
   • Update CHANGELOG.md
   • Commit with spec reference

Validate Spec

When user says "validate spec" or "check spec compliance":

1. Read current spec
2. Analyze implemented code
3. Report discrepancies
4. Suggest spec or code updates

Validation Script

Use scripts/validate_spec.py to check:

• All features in PRD have specs
• All specs have implementation status
• CHANGELOG entries exist for completed features
• Code files reference their specs

Best Practices

1. Atomic Changes: Each todo should be completable in one commit
2. Spec First: Always update spec before major implementation changes
3. Traceability: Every commit message should reference the relevant spec
4. Living Documentation: Specs evolve with the code, not after

Context Preservation

To prevent information loss during Auto-Compact:

• All decisions documented in specs
• Rationale included in CHANGELOG
• Git history provides complete audit trail