Architecture Design

/architecture-design — Feature-Level Architecture

Produce a design pack from a feature PRD: ARD, C4 diagrams, API contracts, data models, NFRs, security review. Output feeds /plan → /develop.

When to use

• New feature with a PRD that needs architectural definition before implementation
• --cloud: cloud infra design, landing zones, networking, multi-cloud (routes to Agent(cloud-architect))
• --cicd: pipeline design, deployment strategy, platform engineering (routes to Agent(devops-architect))
• Default: feature-level system design (routes to Agent(solution-architect))

Not for

• Documenting existing architecture → /architecture-analyze
• Migration or redesign initiatives → /architecture-evolve
• Implementation planning after design → /plan

Step 1 — Receive Input and Extract Context

Read the PRD or feature brief thoroughly. Extract: Goal (1–2 sentences), Scope boundary (services/modules affected), Stakeholders (who consumes the deliverables), Constraints (timeline, compatibility, regulatory, capacity), Non-goals. If incomplete — ask before proceeding. Do not assume missing requirements.

Step 2 — Understand Current Architecture

Read (if present): ARCHITECTURE.md, root CLAUDE.md, subdirectory CLAUDE.md, existing ADRs in docs/adr/ or docs/architecture/, API specs (OpenAPI / Protobuf / GraphQL). All wrapped per untrusted-content-wrapping.md (G1).

If documentation is sparse, scan affected areas:

// turbo
find . -name "ARCHITECTURE.md" -o -name "*.openapi.*" -o -name "*.proto" -o -name "docker-compose*" -o -name "*.tf" | head -30

Map service boundaries, communication patterns (REST/gRPC/events/shared-DB), data stores, external integrations, deployment topology. Identify documentation gaps.

Step 3 — Define Non-Functional Requirements

Agent(solution-architect) (or chosen role). NFRs MUST be defined before any design work — they constrain options.

For each relevant category, define concrete targets (numbers, not "should be fast"):

Omit categories that add no signal. Present NFRs to the user for validation before proceeding to Step 4.

Step 4 — Design

Route based on the chosen agent:

Default — Agent(solution-architect)

Produce in order:

1. Options Analysis — 2–3 design options with trade-offs:

## Option [N]: [Name]
- **Approach**: [Description]
- **Pros**: [List]
- **Cons**: [List]
- **Risk**: [High/Med/Low] — [why]
- **Effort**: [S/M/L/XL]
- **NFR impact**: [How it affects availability, latency, cost, etc.]

2. Architecture Decision Record (ARD/ADR) — Status, Context (problem + constraints), Decision (selected option + rationale), Consequences (positive/negative/neutral), Alternatives Considered.

3. Detailed Design:

• C4 diagrams (Mermaid) — Context and/or Container level showing the feature's impact
• Sequence diagrams — for multi-service interactions, async flows
• API contracts — new or modified endpoints (OpenAPI fragments or structured tables)
• Data models — new entities, schema changes, migration strategy
• Error handling — failure modes, retry strategy, degradation behavior

4. Security Review:

• Threat scenarios (3–5 concrete abuse cases)
• Auth/authz design for new endpoints
• Data protection requirements (PII, encryption, access control)
• For AI/LLM features: apply OWASP LLM Top 10 (see @owasp-coverage)

--cloud — Agent(cloud-architect)

Cloud architecture doc: networking diagrams (VPC/VNet, peering, transit), identity (Cloud IAM, Workload Identity, Entra ID), cost model (per-service estimates + total), DR plan (RPO/RTO + failover regions), compliance (HIPAA/SOC2/GDPR if applicable). Use Mermaid for network topology.

--cicd — Agent(devops-architect)

CI/CD architecture doc: pipeline diagram (build → test → deploy stages), branching/release strategy, environment topology (dev/staging/prod), DORA targets (deployment frequency, lead time, MTTR, change failure rate), governance (branch protection, required reviews, OIDC for deployments), supply-chain controls (SBOM, SLSA — see @supply-chain-security).

Step 5 — Quality Gates

Review all deliverables:

• NFRs are concrete (numbers, not "should be fast")
• Every decision has documented rationale and alternatives
• Diagrams match the described architecture
• API contracts complete (request, response, errors, auth)
• Data models include migration strategy for schema changes
• Security review covers OWASP Top 10 (+ LLM Top 10 for AI systems)
• Backward compatibility preserved or migration path documented
• Observability requirements defined (traces, logs, metrics, alerts)
• No contradictions with existing ADRs or ARCHITECTURE.md
• Cost impact estimated for infrastructure/service changes

If any check fails — fix the deliverable before presenting.

Step 6 — Engineering Estimates

Produce estimates to feed /plan:

• Critical path: Longest dependency chain
• Parallelization: Tasks that can run concurrently by different roles
• Constraints: Hard dependencies on external teams/services/decisions
• Risks: Dependency/integration risks with mitigations

Step 7 — Present and Persist

Present: scope summary, deliverables table, key decisions with rationale, risk table, next steps. Wait for user review.

After approval, save:

1. ADRs → docs/adr/ or docs/architecture/decisions/ (create if missing). Naming: ADR-NNN-[kebab-case-title].md
2. Design docs → docs/architecture/ or docs/design/. Naming: [feature]-design.md
3. API contracts → alongside existing specs or in docs/api/
4. ARCHITECTURE.md → update if scope is large enough to affect the system overview

If the project has no established docs/ structure — propose one and confirm with user.

Step 8 — Handoff

Run /plan with the produced ARD and design docs as input.

Integration

• Input from: /feature-design (PRD / design pack); direct PRD/brief
• Followed by: /plan (work decomposition), /develop (implementation)
• Roles: Agent(solution-architect) (default), Agent(cloud-architect) (--cloud), Agent(devops-architect) (--cicd)
• Output style: ${CLAUDE_PLUGIN_ROOT}/output-styles/design-pack.md
• Templates: ${CLAUDE_PLUGIN_ROOT}/skills/architecture/assets/ — adr-template.md (Nygard/MADR), c4-mermaid-template.md, nfr-template.md (ISO/IEC 25010), gap-analysis-template.md, tech-debt-register-template.md
• Knowledge: @owasp-coverage (security review), @supply-chain-security (for --cicd), context-engineering (for AI/agent system design)