Spec-Driven AI Development
From writing code to architecting systems. Why developers should adopt the new development discipline for the age of AI
The way we build software is fundamentally changing. AI can now write code faster than any human, but there's a catch – it can't decide what to build or how to architect it.
AI has changed the way we build software. We're now using the 50-20-30 principle: Devs spend 50% of their time planning, 20% coding, and 30% validating/testing.
— Ran Aroussi (@aroussi) August 22, 2025
And it works!
👇
This guide presents a systematic approach to AI-assisted development that we've been refining at Automaze, where human developers focus on what they do best (thinking, planning, architecting) while AI handles what it does best (rapid implementation of well-defined specifications).
If you've felt overwhelmed trying to integrate AI into your development workflow, or if you've been burned by AI confidently building the wrong thing, this discipline will help you harness AI's power while maintaining control over your project's direction and quality.
The Reality Check
Why AI Changes Everything (And Nothing)
What AI Can Do Today
✅ Write code faster than any human
- Generate boilerplate in seconds
- Implement algorithms from descriptions
- Create tests from examples
- Refactor with perfect syntax
What AI Cannot Do (Yet)
❌ Make architectural decisions
- Choose between microservices vs monolith
- Decide on caching strategies
- Select the right database for your scale
- Balance tradeoffs between performance and maintainability
- Understand your specific business constraints
The Critical Insight
AI is an incredible executor, but a terrible architect
AI will build exactly what you specify, and it will build it fast. But it will build it wrong if your spec is wrong, and it cannot tell you IF you should build it.
Your job as a developer isn't going away – it's evolving. The old model of 80% coding and 20% thinking is becoming 50% planning, 20% coding, and 30% validating. The developers who thrive will be the ones who embrace this shift.
The New Time Allocation
How Developers Should Spend Their Time in the age of AI
50% Planning & Thinking
This is where your value lives
Deep requirements analysis is now the core of your job. Interview stakeholders multiple times, challenge assumptions aggressively, document edge cases obsessively, and define failure modes explicitly. Your architectural decisions – system boundaries, data flow, scale considerations, and integration points – are what AI cannot do for you.
Every hour spent here saves 10 hours of rework.
10-20% Coding with AI
The execution phase is now the shortest phase
You're now a prompt engineer, not a code writer. A quality controller, not a typist. An architectural guardian, not an implementer. You provide context, and AI generates the implementation.
You: "Implement the cache invalidation strategy from section 3.2"
AI: [Generates 200 lines of code]
You: "Add circuit breaker pattern for Redis"
AI: [Updates with fault tolerance]
20-30% Testing & Fine-Tuning
Trust, but verify everything
This isn't just running tests. It's validating against original requirements, stress testing edge cases, performance profiling, security auditing, and user experience validation. The fine-tuning loop becomes: AI generates, you test against spec, find gaps, update prompts, and repeat until perfect.
The Five-Phase Discipline
A Systematic Approach to AI-Assisted Development
Why "No Vibe Coding"
AI amplifies ambiguity. While humans can infer intent, AI cannot. Humans question weird requirements; AI implements them. A vague instruction to AI produces confidently wrong code. "No vibe coding" isn't about rigidity – it's about clarity.
Phase 1: Brainstorm
Think Deeper Than Comfortable
Spend time exploring the problem space thoroughly. Write down multiple approaches and pick the best ones. Ask "what could go wrong" until you've exhausted possibilities. Consider how this fits your long-term vision, not just immediate needs.
Deliverable: Rough notes, sketches, stakeholder feedback, initial constraints
Phase 2: Document
Write Specs That Leave Nothing to Interpretation
Your PRD must include:
- Problem Statement: Why are we building this?
- Success Metrics: How do we measure success?
- User Stories: Who uses this and how?
- Acceptance Criteria: Specific, testable requirements
- Non-Goals: What we explicitly won't do
- Constraints: Technical, business, and resource limits
❌ Bad: "The system should be fast"
✅ Good: "API responses return within 200ms for 95% of requests under 1000 req/sec load"
Phase 3: Plan
Make Technical Decisions Explicitly
Create your implementation blueprint with technology choices and justifications, system architecture, data models, API contracts, and task decomposition. Always explain the WHY:
Decision: Use PostgreSQL for user data
Why:
- ACID compliance required for financial data
- Complex queries needed for reporting
- Team expertise already exists
- Scaling to 1M users is sufficient
Phase 4: Execute
Build Exactly to Spec
For each task: Load context and spec into AI, generate implementation, review against acceptance criteria, adjust prompts if needed, and commit when criteria are met. You're crafting prompts and providing context, not writing boilerplate or implementing standard patterns.
Phase 5: Track
Maintain Transparent Progress
Document what acceptance criteria were met, what decisions were made, what assumptions changed, and what blockers exist. Every decision documented, every change justified, every deviation explained. Your future self (and AI) will thank you.
Example: Building a Rate Limiter
The Old Way (Pre-AI)
- Quick chat about requirements (30 min)
- Start coding (2 days)
- Realize edge cases throughout
- Add features as discovered (ongoing)
- Test and fix bugs (1 day)
Total: 3-4 days, multiple revisions
The New Way (AI-Assisted)
Day 1 Morning: Brainstorm (2 hours)
- Interview API team about traffic patterns
- Research rate limiting algorithms
- Consider bypass mechanisms
- Document failure modes
Day 1 Afternoon: Document (3 hours)
## PRD: Rat#e Limiter
#### Problem
API abuse is costing $50K/month in infrastructure
#### Success Metrics
- Reduce suspicious traffic by 80%
- Zero impact on legitimate users
- Response time overhead <5ms
#### Acceptance Criteria
- [ ] Implements token bucket algorithm
- [ ] Supports 100K unique keys
- [ ] Redis-backed with local cache fallback
- [ ] Configurable per endpoint and user
- [ ] Graceful degradation on Redis failure
Day 2: Plan and Execute
- Architecture: API Gateway plugin
- Storage: Redis with local LRU cache
- AI generates implementation per spec
- Reviews and adjustments
Day 3: Test and Fine-tune
- Load test with production patterns
- Validate failure behavior
- Performance profiling
Total: 2.5 days, zero architectural revisions
The Mindset Shift
From Coder to Architect-Conductor
You're not a typist anymore. Your identity shifts from "I write code" to "I design systems and ensure quality."
The Skills That Matter Now
- Systems thinking - Understanding how pieces connect
- Clear communication - Writing specs AI can't misinterpret
- Edge case imagination - Thinking of what could go wrong
- Quality judgment - Knowing when code is production-ready
- Prompt engineering - Getting AI to build what you envisioned
What to Focus On
Invest in: System design, technical writing, domain modeling, requirements analysis, test strategy
Worry less about: Syntax memorization, algorithm implementation, boilerplate patterns, code formatting
The uncomfortable truth: AI won't replace developers, but developers using AI will replace developers who don't. More specifically, developers who can architect and specify will replace developers who only code.
Context Optimization with Sub-Agents
Scaling AI Development Without Context Explosion
As projects grow, context overwhelms. Claude's context window is large but not infinite, and full project context slows responses while increasing costs.
The Sub-Agent Pattern
Main Agent (Orchestrator)
├── API Agent (owns backend context)
├── UI Agent (owns frontend context)
├── Data Agent (owns database context)
└── Test Agent (owns test context)
Each sub-agent gets ONLY relevant context. The API agent knows about endpoints and authentication but not CSS or frontend state. The UI agent knows components and design systems but not database schemas.
Real Impact
Without Sub-Agents:
- Context: 100K tokens
- Response time: 45 seconds
- Cost: $0.50 per interaction
- Accuracy: Often references wrong components
With Sub-Agents:
- Context: 10K tokens per agent
- Response time: 8 seconds
- Cost: $0.08 per interaction
- Accuracy: High, focused domains
Sub-Agent Communication
Sub-agents return structured summaries to the main orchestrator:
{
"agent": "api",
"task": "auth-endpoints",
"status": "complete",
"decisions": [
"Used JWT for stateless auth",
"Implemented refresh token rotation"
],
"interfaces": {
"endpoints": ["/auth/login", "/auth/refresh"],
"errors": ["AUTH_001", "AUTH_002"]
},
"concerns": [
"Need Redis for rate limiting"
]
}
Use sub-agents when you have clear domain boundaries, large codebases (>100 files), or specialized domains. Avoid them for small scripts or tightly coupled systems.
Introducing CCPM
A Tool That Enforces This Discipline
Good intentions aren't enough. It's easy to skip documentation under pressure, tempting to "just start coding," and difficult to coordinate multiple AI agents.
CCPM (Claude Code Project Management) is a tool that enforces this discipline:
- Forces the five phases - Can't code without a spec
- Maintains context - No more re-explaining to AI
- Enables parallel AI agents - Multiple AIs on one project
- Creates audit trails - Every decision tracked in GitHub
- Integrates with existing tools - GitHub Issues as database
Quick Example
# Force#s you to brainstorm and document
/pm:prd-new feature-name
## Forces you to plan
/pm:prd-parse feature-name
## Enables parallel execution
/pm:epic-oneshot feature-name
/pm:issue-start 1234 # AI agent 1
/pm:issue-start 1235 # AI agent 2
CCPM doesn't change the discipline – it enforces it. You could follow this process manually, but it does make it systematic and repeatable, especially powerful for team coordination.
Common Questions
"This seems like a lot of overhead"
The overhead is front-loaded. You'll spend 2x time planning but 0.2x time debugging and reworking. Net win: 50% faster delivery with higher quality.
"What if requirements change?"
They will. But now changes are explicit, documented, and AI can refactor faster than you can type. Changes are less painful when specs exist.
"What about exploratory coding?"
Still valuable! But timebox it, call it what it is (research), and don't ship it. Use exploration to inform your spec, then build properly.
"Is this just waterfall?"
No. You can iterate, but each iteration follows the discipline. Think of it as "structured agility" – flexible in direction, disciplined in execution.
Your Next Steps
Start Small
- Pick one small feature in your current project
- Write a complete PRD before coding
- Time yourself through all five phases
- Use AI for execution following your spec exactly
- Compare to your normal process
Build the Habit
- Track your time allocation – aim for 50/20/30
- Build your edge case muscle – list 10 for every feature
- Practice prompt engineering – get faster at directing AI
- Share your specs – get feedback from teammates
The Bottom Line
The future belongs to developers who can:
- Think deeply about problems
- Specify solutions precisely
- Orchestrate AI execution
- Validate quality rigorously
The question isn't whether to adopt this discipline. The question is whether you'll adopt it before your competition does.
Share Your Experience
This guide represents our current understanding of how to effectively blend human expertise with AI capabilities, but we know we're just scratching the surface.
If you're implementing these practices, hitting roadblocks, or discovering better patterns, I'd love to hear from you.
Share your experiences, successes, and failures – the entire developer community benefits when we learn together.
Remember: AI amplifies your decisions. Make them good ones.
Links
- CCPM Tool: github.com/automazeio/ccpm
Updated on 22 August 2025.
For the latest version and comments, please see:
https://aroussi.com/post/spec-driven-ai-development