SDD Planning Skill

Transform specifications into actionable technical plans.

When to Use

•Spec exists but plan doesn't
•Designing system architecture
•Breaking down features into components
•Preparing for implementation phase
•After research is complete

Planning Protocol

Step 1: Understand Requirements

•Read spec.md thoroughly
•Note functional requirements and acceptance criteria
•Identify non-functional requirements (performance, security)
•Review research findings if available

Step 2: Design Architecture

•Identify major components
•Define component responsibilities
•Design interfaces and contracts
•Plan data flow

Step 3: Select Technology

•Evaluate options against requirements
•Consider existing codebase stack
•Document rationale for choices

Step 4: Plan Implementation

•Break into phases (Setup → Core → Integration → Polish)
•Identify dependencies between components
•Estimate effort for each phase

Step 5: Assess Risks

•Identify technical risks
•Plan mitigations
•Note assumptions

Plan Output Format

markdown

# Technical Plan: [Task ID]

## Overview
[2-3 sentence summary of approach]

## Architecture

### System Diagram
```mermaid
[architecture diagram]

Components

Component	Responsibility	Dependencies
[name]	[what it does]	[depends on]

Technology Stack

•Frontend: [choice] - [rationale]
•Backend: [choice] - [rationale]
•Database: [choice] - [rationale]
•Infrastructure: [choice] - [rationale]

API Design

[Key endpoints and contracts]

Data Models

[Entity definitions and relationships]

Security Considerations

Performance Targets

Metric	Target	Approach
[metric]	[value]	[how to achieve]

Implementation Phases

Phase 1: Setup

•[task with estimate]

Phase 2: Core

•[task with estimate]

Phase 3: Integration

•[task with estimate]

Phase 4: Polish

•[task with estimate]

Risks

Risk	Probability	Impact	Mitigation
[risk]	[H/M/L]	[H/M/L]	[approach]

Testing Strategy

•Unit: [approach]
•Integration: [approach]
•E2E: [approach]

Open Questions

•[questions needing answers before implementation]

code


## Diagram Templates

See `assets/diagram-templates.md` for common architecture diagram patterns.

## Integration

- Input from: `sdd-research` skill, `sdd-explorer` subagent
- Output to: `/tasks` command, `sdd-implementer` subagent
- Works with: `sdd-planner` subagent for complex architectures
- Use the ask question tool for architectural decisions with significant tradeoffs