Spec First Sdlc

Spec-First SDLC

A structured software development lifecycle where specifications drive implementation. Human writes intent; Claude produces design documents, implementation specs, code, and tests—with review gates at each phase.

Workflow Overview

Intent & Constraints (human)
        ↓
High-Level Design (Claude) ←→ Human Review
        ↓
ADR-Lite (Claude) ←→ Human Review
        ↓
Revised HLD (Claude)
        ↓
Executable Implementation Spec (Claude) ←→ Human Review
        ↓
Code Generation (Claude)
        ↓
Validation Tests (Claude)

Phase Details

Phase 1: Intent and Constraints

Owner: Human
Output: docs/intent-and-constraints.md

Human provides:

• Problem statement and goals
• Functional requirements
• Non-functional constraints (performance, security, scalability)
• Known boundaries and limitations

Phase 2: High-Level Design (HLD)

Owner: Claude
Input: Intent and constraints document
Output: docs/high-level-design.md
Template: See references/hld-template.md

Generate HLD covering:

• System architecture and component breakdown
• Data flow and integration points
• Technology choices (with rationale)
• Open questions section listing:
  • Ambiguities in requirements
  • Design choice alternatives with default recommendations
  • Areas needing clarification

Wait for human review and agreement before proceeding.

Phase 3: Architecture Decision Record Lite (ADR-Lite)

Owner: Claude
Input: Approved HLD + human feedback
Output: docs/adr-lite.md
Template: See references/adr-template.md

For each significant decision, document:

• Decision: What was decided
• Alternatives: Options considered
• Rationale: Why this choice (reference constraints from intent doc)
• Consequences: Trade-offs and implications

Each ADR entry must explicitly reference:

• The HLD open question it resolves
• Relevant constraints from intent document that influenced the decision

Wait for human review and agreement before proceeding.

Phase 4: HLD Revision

Owner: Claude
Input: Approved ADR-Lite
Output: Updated docs/high-level-design.md

Revise HLD to:

• Resolve open questions by referencing ADR-Lite decisions
• Add traceability links (e.g., "See ADR-001")
• Remove ambiguities

Phase 5: Executable Implementation Specification (EIS)

Owner: Claude
Input: Revised HLD + ADR-Lite
Output: docs/implementation-spec.md
Template: See references/eis-template.md

Specify implementation details:

• API contracts: Endpoints, request/response schemas, error semantics, auth
• State machines: Key business entity lifecycles with transitions and guards
• Persistence: File layouts, database schemas, data models
• Module boundaries: Interface contracts between components

Wait for human review and agreement before proceeding.

Phase 6: Code Generation

Owner: Claude
Input: Approved EIS
Output: Source code in src/

Implement code that:

• Adheres strictly to EIS contracts
• Includes documentation comments explaining design rationale
• Follows project's coding conventions
• References relevant ADR decisions in comments where appropriate

Phase 7: Validation

Owner: Claude
Input: Implementation + Intent document
Output: Tests in tests/

Generate comprehensive tests:

• State transition tests: Verify entity lifecycle behaviors
• Contract tests: Validate API request/response schemas
• Negative tests: Error handling, invalid inputs, edge cases
• Concurrency tests: Race conditions, deadlocks (where applicable)

Tests should trace back to original intents and constraints.

Review Gates

Never proceed to the next phase without explicit human approval. At each gate:

1. Present the deliverable with a summary of key points
2. Highlight decisions or areas that may need discussion
3. Ask: "Ready to proceed to [next phase], or would you like changes?"

Mid-Workflow Entry

When user provides existing artifacts and wants to continue from a specific phase:

1. Identify Entry Point

Determine which phase to start from based on what artifacts exist:

• Has intent doc only → Start at Phase 2 (HLD)
• Has intent + HLD → Start at Phase 3 (ADR-Lite)
• Has intent + HLD + ADR → Start at Phase 4 (HLD Revision) or Phase 5 (EIS)
• Has complete specs → Start at Phase 6 (Code) or Phase 7 (Validation)

2. Assess Existing Artifacts

Before generating the next artifact, review provided documents for:

• Completeness: Are required sections present?
• Consistency: Do artifacts align with each other?
• Open items: Are there unresolved questions that block progress?

If gaps or inconsistencies found:

"I reviewed [artifact]. Before proceeding to [next phase], I noticed:
- [Gap or inconsistency]
Would you like me to address this first, or proceed with assumptions?"

3. Establish Traceability

When entering mid-workflow, explicitly map existing artifacts:

• Extract key decisions/constraints from provided docs
• Reference them when generating new artifacts
• Note any assumptions made due to missing context

4. Resume Normal Flow

After assessment, continue with standard phase sequence and review gates.

File Structure

project/
├── docs/
│   ├── intent-and-constraints.md
│   ├── high-level-design.md
│   ├── adr-lite.md
│   └── implementation-spec.md
├── src/
│   └── [implementation files]
└── tests/
    └── [test files]