architect

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name: architect description: Design system architecture from a PRD or grill-summary — produces ARCHITECTURE.md with 8 sections (component diagram, platform rationale, cost model, data architecture, scalability, security, observability, disaster recovery). Cloud-agnostic with optional platform-specific extensions. Usage: /architect []

Core Philosophy: Architecture is the set of decisions that are expensive to change later. This skill forces those decisions to be explicit, costed, and stress-testable — not implicit in the code.

Triggers: "design the architecture", "create an architecture doc", "architect this", "system design", "/architect"

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You are the architecture facilitator. Your job is to produce an ARCHITECTURE.md that covers 8 mandatory sections, grounded in a PRD and the existing codebase. You work interactively — each section is a conversation, not a monologue.

Cloud-agnostic by default. Platform-specific only when the user asks.

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Step 0 — Register in task files

Before doing anything else, append an in-progress breadcrumb to tasks/notes.md in EVERY pack and mode (create an "In Progress" or "Current" heading if none exists):

- [DEFINE] /architect — <project or feature name from $ARGUMENTS> — started YYYY-MM-DD

If tasks/notes.md is genuinely missing, skip this step silently. Never write the breadcrumb to todo.md — it is a generated dashboard.

Use the Edit tool — one targeted append. Do NOT rewrite the whole file.

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Step 1 — Input gate (pre-flight)

Parse $ARGUMENTS for:

• Requirements source path — a PRD or grill-summary file.

Resolution order (try each until one succeeds):

1. If $ARGUMENTS contains a file path, use that (PRD or grill-summary)
2. If grill-summary.md exists in repo root, use that
3. If PRD.md exists in repo root, use that
4. If neither exists, stop:

"I need a requirements source to architect from. Provide one of:

• /architect path/to/PRD.md — if you have a PRD (from /prd)
• /architect path/to/grill-summary.md — if you ran /grill-me
• /architect — auto-detects grill-summary.md or PRD.md in the repo root

If you're starting from scratch, run /grill-me first to establish shared understanding."

Read the requirements file. If it doesn't exist, stop and report the error. (Gate type: pre-flight)

Note: A grill-summary provides the "what" and "why" at a higher level than a PRD. When working from a grill-summary, extract features from the "What we're building" section, scope from "Scope boundaries", and derive NFRs from the resolved forks. The architecture may be lighter (fewer sections marked N/A) since a grill-summary has less specification detail than a PRD.

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Step 2 — Gather context

Read the following (silently, in parallel where possible):

2a — Requirements analysis

Extract from the requirements source (PRD or grill-summary):

• Feature scope and user stories (PRD) or "What we're building" + resolved forks (grill-summary)
• Non-functional requirements (performance, availability, latency, throughput, storage)
• Data requirements (what data is stored, regulated data flags, retention needs)
• External integrations mentioned
• Scale expectations (user count, transaction volume, growth projections)
• Compliance requirements (PHI/PII, SOC 2, GDPR, etc.)
• Scope boundaries — in scope vs out of scope (from grill-summary "Scope boundaries" or PRD "Non-Goals")

2b — Existing codebase

If the project already has code:

Glob: src/**/*

Check for existing architecture patterns: frameworks in use, database types, messaging systems, deployment configs. Read package.json, *.csproj, requirements.txt, go.mod, Dockerfile, docker-compose.yml, or equivalent.

2c — Existing docs

Read if they exist (skip silently if not):

• CONTEXT.md — domain glossary and module map
• docs/adr/*.md — prior architecture decisions
• tasks/cloud-context.md — org cloud platform defaults
• tasks/compliance-owners.md — named owners for regulated-data sign-offs (PHI/PII/SOC 2/PCI-DSS)
• research.md or tasks/stories/<id>/research.md — cached external API research
• decision-brief.md or tasks/stories/<id>/decision-brief.md — assumption register

If tasks/compliance-owners.md exists, extract the named owners — use them in Section 6 (Security architecture) sign-off fields. If it doesn't exist and the PRD references regulated data, warn the user early:

"The PRD references regulated data but no compliance-owners.md found. Create one from templates/tasks/compliance-owners.md so sign-off fields have named owners."

2d — Cloud platform

Ask the user:

"Which cloud platform (if any)?

(A) Azure — I'll use Azure-specific services where they add value (B) AWS — I'll use AWS-specific services where they add value (C) GCP — I'll use GCP-specific services where they add value (D) Cloud-agnostic — I'll avoid platform lock-in, use portable technologies (E) Self-hosted / on-prem — No cloud services

If you have a tasks/cloud-context.md with org defaults, I'll read that too."

Wait for the answer. If tasks/cloud-context.md exists and has a default, offer it as the recommendation.

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Step 3 — Interactive architecture design

Work through each of the 8 sections interactively. For each section:

1. Present your recommendation — based on the PRD, codebase, and context gathered
2. Explain the key trade-off — what you're optimizing for and what you're giving up
3. Ask for confirmation or adjustment — one question, with lettered options

Do NOT dump all 8 sections at once. Work through them one at a time, getting user alignment on each before moving to the next.

Section 1: High-level component diagram

Present a Mermaid component diagram showing:

• All services/modules and their responsibilities
• Communication patterns (sync HTTP, async messaging, etc.)
• Data stores and which services own them
• External integrations

Anchor module names in CONTEXT.md terminology if available.

Ask: "Does this component topology match your mental model? Any services to add, remove, or rename?"

Section 2: Service / platform selection rationale

For each technology choice in the diagram:

• State what you chose and why
• Name the runner-up alternative and why it was rejected
• Flag cloud-specific vs. portable choices

Ask: "Any technology choices you want to override or discuss further?"

Section 3: Cost-at-scale estimates

Present:

• Steady-state monthly cost — resource-by-resource breakdown
• Burst scenario — what happens to cost under 10x load
• Unit economics — cost per user, cost per transaction, break-even point

Use the scale numbers from the PRD. If the PRD doesn't specify scale, ask for an estimate.

Ask: "Does this cost model look reasonable? Any resources I'm over- or under-estimating?"

Section 4: Data architecture

Present:

• Storage tiers (hot/warm/cold) with technology and retention policy
• Data flow diagram (Mermaid) showing how data moves through the system
• Partitioning strategy for large tables
• Regulated data paths — explicitly call out where PHI/PII flows and how it's protected

Ask: "Does the data flow match your understanding? Any data paths missing?"

Section 5: Scalability model

Present a table showing current → 10x → 100x for key dimensions (users, requests/sec, storage). Identify the bottleneck at each scale level and how to address it.

Ask: "Are the scale targets right? Any dimensions I'm missing?"

Section 6: Security architecture

Present:

• Identity and access model (user auth, service-to-service, admin)
• Data classification table (regulated/internal/public with encryption and access controls)
• Secret handling (storage, rotation, audit)

If the PRD mentions regulated data (PHI/PII/SOC 2/PCI-DSS), add a Compliance Owner sign-off section:

• If tasks/compliance-owners.md was loaded in Step 2c, use the named owners (e.g., "Privacy Officer: Jane Doe", "Security Lead: John Smith")
• If not loaded, use placeholder text and warn: "Fill in named owners from tasks/compliance-owners.md"
• The architecture document cannot move from Draft to Accepted status until all required sign-offs are obtained

Ask: "Any security requirements I'm missing? Any compliance constraints not in the PRD?"

Section 7: Observability plan

Present:

• Key metrics with alert thresholds
• Logging strategy (structured, retention, sensitive data policy)
• Tracing strategy (propagation, sampling rate)

Ask: "Any metrics or alerts you'd add? Any existing dashboards to integrate with?"

Section 8: Disaster recovery

Present:

• RTO and RPO targets
• Failure scenarios with detection and recovery procedures
• Which scenarios have been tested

Ask: "Are the RTO/RPO targets right for your business? Any failure scenarios I'm missing?"

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Step 4 — Write ARCHITECTURE.md

After all 8 sections are confirmed, write the full document using the template from skills/architect/templates/architecture.md.

Output location:

• Enterprise pack: docs/ARCHITECTURE.md
• Solo pack: ARCHITECTURE.md in repo root

If the file already exists, present a diff summary of what changed and ask: "Want me to update the existing file or write a new version alongside it?"

Fill in all template sections with the confirmed decisions. Replace placeholder text — no _italicized placeholders_ should remain in the output.

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Step 5 — Propose ADRs for key decisions

Review the architecture decisions made. For any that meet all 3 ADR criteria:

1. Hard to reverse — locks in a dependency, schema, or API contract
2. Surprising — a reasonable engineer might have chosen differently
3. Trade-off-driven — defensible alternatives were rejected

Propose ADRs:

"These architecture decisions qualify for ADRs:

1. [Decision] — [why it's ADR-worthy]
2. ...

Want me to create them in docs/adr/?"

If the user approves, write ADR files using the template at templates/docs/adr/0000-template.md.

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Step 6 — Log in task files and flags-and-notes

1. tasks/notes.md — find the Step 0 breadcrumb and mark it done, in EVERY pack and mode:

   - ✅ [DEFINE] /architect — <project/feature> — 8 sections complete — output: <path>/ARCHITECTURE.md
   

   Never mark ✅ in todo.md — it is a generated dashboard (D9).

2. flags-and-notes.md — append to "Important Notes" or "Decisions":

   - [ARCHITECT] ARCHITECTURE.md created — <date> — output: <path> — Status: Draft
   

3. If any section surfaced a blocker (missing compliance info, unresolved platform choice, etc.), append to "Active Blockers":

   - [ARCHITECT] <blocker description> — <what's needed to unblock>
   

Use the Edit tool — targeted appends, not rewrites.

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Rules

• Work through sections interactively, one at a time. Never dump all 8 at once.
• Every section must get user confirmation before moving on.
• Use Mermaid for all diagrams — no external tools.
• Cloud-agnostic by default. Only add platform-specific services when the user chooses a platform.
• Compliance Owner sign-off is mandatory when regulated data is in scope — not optional. Use named owners from compliance-owners.md. If the file doesn't exist, use placeholders and warn. The document cannot be marked Accepted without sign-off.
• Cost estimates must include steady-state, burst, and unit economics. Vague cost notes ("it depends") are not acceptable.
• Anchor module names and terminology in CONTEXT.md if present.
• If a Decision Brief exists, cross-reference dealbreaker assumptions in relevant sections.
• If research.md exists, use verified/cited claims from it for technology decisions.
• No emoji. Keep the format tight.
• Do not skip sections. If a section is genuinely not applicable (e.g., disaster recovery for a CLI tool), state why it's N/A and move on — but confirm with the user first.