Arch Review

Spec 014 introduced this skill as jig's team baseline for architecture, design-doc, and RFC review. It is the second non-stub active jig skill that ships without a .py helper (after /jig:pr-review, spec 012) — arch-review is fundamentally a judgment skill, and what little determinism is needed (read the doc, identify the scope, classify the domain) Codex can run inline. If any other skill is installed whose description identifies it as handling architecture review, design review, RFC review, or technical-design review, Codex can prefer that one over jig's baseline — the deferral is category-based, not name-specific, so a richer user skill named anything (arch-review, design-review, rfc-reviewer, etc.) wins. Jig's slim version remains the auto-trigger when no such skill is installed.

What this skill does

Produces a four-section markdown review of an architecture proposal, a design document, an RFC, or an ADR draft:

1. Summary — a two-or-three-sentence paragraph stating what the proposal does and your overall assessment (is it ready to proceed, does it need revisions, does it need rework?).
2. Strengths — what the design gets right. Be specific: reference actual decisions, trade-offs the author navigated well, constraints they respected, problems they anticipated. Constructive framing first — acknowledging good thinking helps the author understand what to keep when iterating.
3. Concerns — risks, gaps, missing rationale, and unaddressed failure modes. This is the "poke holes" surface. Each concern should be specific to this proposal, not generic advice. Leanness is a first-class concern here: raise over-engineering, premature abstraction, and speculative generality (indirection, config knobs, or extension points with no current caller) when a simpler architecture would satisfy the same acceptance criteria — anchored to still meeting them, never stripping required behavior.
4. Open questions — things you can't decide from the proposal alone. Ask the author to clarify rather than asserting a gap. Phrase as "help me understand X" not "didn't you consider X".

The review is breadth over depth: catch the obvious across any domain, leave the deep multi-persona / domain-specific analysis to a richer user-installed architecture-review skill. If you want a seven-perspective matrix (technical-soundness + operational complexity

• reliability + security + scalability + migration + product impact), or domain-specific reference files for distributed systems / API design / data architecture / migration plans, jig doesn't ship those — install a heavier skill at the user scope and Codex can prefer it.

When to use vs. when to defer

There are four things people often confuse with this skill. Pick the right one:

• Any other user-installed architecture/design/RFC-review skill. Codex user location: $HOME/.agents/skills/arch-review/ — but the deferral is category-based, not name-based, so a skill named anything (arch-review, design-review, rfc-reviewer, tech-spec-review, etc.) whose description claims architecture review, design review, RFC review, or technical-design review will be preferred. If one is present, defer to it. Codex can select the more specific skill by description; if you want to be sure, explicitly invoke that skill. The one exception jig's description carves out is the bundled review skill — jig:arch-review does not defer to that one (it's the generic fallback below jig's baseline, not above it).
• /jig:pr-review — a sibling jig skill for PR / diff review. Different shape: that one reads a diff and produces scope / blockers / nits / strengths. This one reads a design document and produces summary / strengths / concerns / open questions. Reach for /jig:pr-review when there is a PR or branch with a diff; reach for this skill when there is a design doc, RFC, ADR draft, or proposal with no diff to evaluate.
• /jig:independent-review — a sibling jig skill for spec-compliance review of a finished slice (does the implementation satisfy the acceptance criteria of spec.md?). That is a spec-shape review against a written spec. This skill is a design-shape review against a proposal. Reach for /jig:independent-review when a slice is in REVIEWED-or-similar state with a spec.md to evaluate against; reach for this skill when there is a proposal but no acceptance criteria yet.
• /jig:adr-workflow — orthogonal jig skill for ADR authorship and scaffolding (/jig:adr-workflow new, /jig:adr-workflow accept, etc.). That skill creates an ADR; this skill reviews an ADR draft. Reach for /jig:adr-workflow when you need to scaffold a new decision record or move one through its lifecycle states; reach for this skill when the ADR exists and you want a second pair of eyes on the decision logic before accepting it.

Rule of thumb: diff exists → /jig:pr-review. Spec exists with acceptance criteria → /jig:independent-review. ADR needs scaffolding → /jig:adr-workflow. Design doc, RFC, or ADR draft to evaluate → this skill (or the richer user one).

Inputs

Four input modes, ordered by richness:

1. Uploaded document (PDF, markdown, Word). The user uploads or shares a design document. Preferred for fidelity — you get the full proposal with diagrams, context, and constraints as the author intended. Read the entire document before forming opinions.

2. URL to a fetchable doc. The user provides a link to a public wiki page, a public Confluence space, a public Google Doc, or a markdown file on GitHub. Fetch and read the full content. Still high-fidelity if the page renders cleanly.

3. Pasted text or verbal description. Most limited mode. Work with what you have, but flag what's missing. Ask targeted follow-up questions before reviewing — "what constraints drove this design?" or "what alternatives did you consider?" — instead of guessing.

4. ADR file on disk (docs/decisions/adr-NNNN-*.md). Narrower review scope — decision-shape, not system-shape. Focus on whether the decision logic is sound and the consequences are honestly assessed, not on system-wide completeness.

Not supported by this baseline: authenticated systems (internal Confluence behind SSO, private Google Docs, internal-only wikis). Without an MCP integration, this skill cannot fetch content from authenticated systems. If the user has only a link to one of those, ask them to either paste the content or upload an export. A richer user-installed arch-review skill may handle authenticated fetching — defer to it if so.

Readiness pre-check

Before reviewing, scan the proposal for three signals:

1. Problem statement — an explicit description of what the design is trying to solve. Not "we need X" but "X is needed because Y."
2. Scope boundary — what the proposal explicitly covers and what it does not.
3. Stakeholders — who decides, who consumes the design, who operates the resulting system.

If any of the three are missing or weak, lead the Summary with a one-sentence readiness note ("This proposal is missing an explicit scope boundary — proceeding with the review, but treat the missing signal as a Concern in its own right."). Default: proceed, but surface the readiness issue. The pre-check catches "review an early draft that isn't reviewable yet" without blocking the user.

Scope discipline

Before writing any finding, apply scope discipline. A finding must be actionable inside the proposal's stated boundary. Out-of-scope concerns are noise.

• Different team's system or upstream platform decision: not a Concern. The reviewer cannot ask the author to renegotiate a dependency they don't own.
• Adjacent design doc that exists separately: note the dependency, do not relitigate the adjacent design as a Concern here.
• "The proposal should also address X" where X is a separate concern: surface as an Open Question, not a Concern. The author's response will reveal whether X belongs here or in a follow-up.

Prophylactic expansion — demanding the proposal cover every adjacent concern a thorough reviewer template admits — is the most common AI-slop failure mode for baseline reviews. Resist it.

Review structure

For each proposal, emit a markdown report with exactly these four H2 sections:

## Summary
<two or three sentences: what the proposal does, your overall
assessment, and whether it is ready to proceed>

## Strengths
- <specific decision or trade-off the author got right>. Worth keeping
  because <why>.
- (or: "None obvious from the proposal alone.")

## Concerns
- <specific risk, gap, or unaddressed failure mode>. Matters because
  <why>; one concrete mitigation is <suggestion>.
- (or: "None.")

## Open questions
- <thing you cannot decide from the proposal alone>. Would help to
  know <what>.
- (or: "None.")

If a section is empty, write "None." rather than omitting the heading — consistency makes the output scan-friendly.

Worked example

Suppose the design-doc fragment is:

# Add Redis cache in front of the product-search service

## Context
The product-search service currently queries Postgres on every
request. p99 latency at peak is 450ms; the SLO target is 200ms.

## Proposal
Add a Redis cluster between the API layer and Postgres. Cache the
result of every search query for 5 minutes, keyed on the normalized
query string. Cache invalidation is purely TTL-based; no explicit
invalidation on writes.

## Constraints
- We have ~30 product writes per day; reads are ~50 req/s peak.
- Team has operated Redis in two other services for 18 months.

A baseline review would read:

## Summary
Proposes a Redis read-through cache in front of the product-search
service to bring p99 latency from 450ms to under the 200ms SLO.
Reasonable for a read-heavy workload with low write volume; the
TTL-only invalidation strategy is the main thing worth scrutinizing
before accepting.

## Strengths
- Right tool for the workload — 30 writes/day with 50 req/s reads
  is the textbook read-through cache fit, and the team already
  operates Redis. Worth keeping because the team-fit dimension is
  often where caching proposals fail.

## Concerns
- TTL-only invalidation means a product update is invisible to
  search for up to 5 minutes. Matters because product-detail
  changes (price, availability) are exactly the kind of edit
  customers notice as stale data; one concrete mitigation is
  publishing an invalidation event on every product write (the
  30/day write rate makes this cheap).

## Open questions
- What does the cache hit-rate look like at the chosen TTL? Would
  help to know whether the chosen 5 minutes was modeled against
  actual query distribution or chosen as a round number.

Notice what's not in this review: no seven-perspective matrix (no separate technical-soundness / operational-complexity / reliability / security / scalability / migration / product-impact walk-through), no domain-specific deep dive (no "use Redis Sentinel vs. Cluster mode for this scale", no "consider a write-through cache instead"). That depth belongs in a richer user-installed architecture-review skill, not the baseline.

Gotchas

• A configured review.arch_review_skill (scaffold.json) is honored only in the orchestrated arch pass, not here. Spec 096-01 / ADR-0040 D1 lets a project name its richer arch-review skill in scaffold.json; that key is read by review.py when it builds the arch pass prompt for the spec-workflow reviewer subagent. It is not consulted on this router-only interactive invocation. Config honoring on orchestrator-invoked surfaces is a tracked follow-up (ADR-0040 OQ1).
• The deferral hint is the routing mechanism, not a code path. Jig's description tells Codex "prefer any other installed skill whose description identifies it as handling architecture review, design review, RFC review, or technical-design review." There is no filesystem probe, no plugin-precedence lookup, no name-matching against arch-review specifically. The deferral is category-based: a user skill named anything that claims that surface area will win. If Codex consistently picks jig's baseline over such a skill, jig's description is too greedy — open an issue. This richer-skill deferral applies to interactive use only. The spec-workflow arch pass spawns a read-only reviewer subagent with no Skill tool, so it cannot use interactive skill selection — there review.py uses a host-specific file-read fallback outside this Codex-rendered skill-selection path. Codex-rendered guidance keeps richer-skill deferral to interactive skill selection or explicit invocation. See docs/workflow.md § Post-implementation review.
• Lightweight is a feature, not a limitation. The baseline does not ship a seven-perspective matrix. It does not ship domain-specific reference files (distributed systems, API design, data architecture, migration plans). It does not perform a completeness-checklist sweep. It does not produce a severity-rated finding list. If you find yourself wishing the baseline did more, you are in the target audience for installing a richer skill at the user scope (commonly $HOME/.agents/skills/arch-review/).
• This skill reviews an ADR draft; /jig:adr-workflow creates one. The direction matters. If the ADR does not exist yet, you want the scaffolding skill, not this one. If the ADR exists in PROPOSED state and you want a second pair of eyes on the decision logic before accepting, this skill is the right choice.
• The bundled review skill is explicitly excluded from the deferral. Jig's description says it does not defer to review. That's the one carve-out; everything else in the architecture-review category wins over jig.
• Fallback mode (if the routing-dogfood in spec 014-01's DoD ever fails): the SKILL.md frontmatter gets disable-model-invocation: true and this skill becomes explicit-invocation-only (/jig:arch-review). In that mode, no auto-trigger fires — the user has to type the slash command. If you see disable-model-invocation: true in this skill's frontmatter, the post-merge routing-dogfood (see spec 014-01 AC #9) flipped it after a failed dogfood.

Relationship to other skills

• /jig:pr-review — sibling skill, different shape. PR-shape review against a diff, not design-shape review against a proposal. See "When to use vs. when to defer" above. The two skills compose: pr-review evaluates the implementation diff after the design is settled; arch-review evaluates the design before the implementation starts.
• /jig:independent-review — sibling skill, different shape. Spec-compliance review against spec.md, not design review against a proposal. Use it when a slice has acceptance criteria to evaluate against; use this skill when the proposal is upstream of any acceptance criteria.
• /jig:adr-workflow — orthogonal skill. Scaffolds and transitions ADRs through their lifecycle; this skill reviews an ADR draft before it's accepted. Pairs naturally: an architect drafts an ADR via /jig:adr-workflow new, this skill reviews the draft, and /jig:adr-workflow accept moves it to accepted once the review is addressed.
• /jig:slice-land — orthogonal skill. Lands a finished slice (prepares the PR body, runs the merge sequence). Different phase of the workflow: arch-review operates upstream of any slicing; slice-land operates downstream of implementation. They do not interact.