System Design

Design Principles

• Modularity: Separated concerns for independent testing and development
• Simplicity: Minimal complexity appropriate for startup resources
• Scalability: Designed to grow with user base
• Cost-effectiveness: Optimized for startup budget

Input

$ARGUMENTS

• prd.md

  - Product requirements (required)

• idea.md

  ,

  validate.md

  - Additional context (optional)

Workflow

Phase 1: Setup & Validation

1. Verify

   prd.md

   exists
2. Read supporting docs if present
3. Read references/tech-stack.md for technology recommendations
4. Backup existing

   tad.md

   if present

Phase 2: Extract Context

• Product name and vision
• Core features and requirements
• User flows
• Non-functional requirements
• Third-party integrations
• Analytics requirements

Phase 3: Clarify Architecture

Phase 4: Research & Validation

1. Technology Stack: Validate choices against industry standards
2. Infrastructure: Compare hosting for cost and scalability
3. Security: Review OWASP guidelines for chosen stack
4. Risk Assessment: Identify bottlenecks, vendor lock-in
5. Holistic Review: Ensure PRD alignment and startup feasibility

Phase 5: Generate TAD

tad.md

1. System Overview - Purpose, scope, PRD alignment
2. Architecture Diagram - Mermaid diagrams for system and flows
3. Technology Stack - Frontend, backend, database, infrastructure, DevOps
4. System Components - Modular design with interfaces and dependencies
5. Data Architecture - Schema, models, flows, storage
6. Infrastructure - Hosting, environments, scaling, CI/CD, monitoring
7. Security - Auth, authorization, data protection, API security
8. Performance - Targets, optimization strategies, caching
9. Development - Environment setup, project structure, testing, deployment
10. Risks - Risk matrix with mitigations
11. Appendix - Research insights, alternatives, costs, glossary

Phase 6: Output

1. Write

   tad.md

   to project folder
2. Summarize architecture decisions
3. Highlight modular design benefits
4. List cost estimates by phase
5. Suggest next steps (setup dev environment, create tasks)

Modification Mode

1. Create timestamped backup
2. Ask what to modify (stack, infrastructure, security, data, scaling)
3. Apply changes preserving structure
4. Update revision history

Guidelines

• Practical: Implementable solutions for startups
• Cost-conscious: Consider budget implications
• Modular: Emphasize separation of concerns
• Specific: Concrete technology choices
• Visual: Include mermaid diagrams