Pr Review

Spec 012 introduced this skill as jig's team baseline for PR and code review. It is the first non-stub active jig skill that ships without a .py helper — pr-review is fundamentally a judgment skill, and the determinism it needs (git diff, file-type detection) Claude can run inline. If any other skill is installed whose description identifies it as handling PR review, code review, or diff review, the Claude Code skill router prefers that one over jig's baseline — the deferral is category-based, not name-specific, so a richer user skill named anything (pr-review, code-reviewer, team-pr, 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 a pull request, a diff, or a branch's accumulated changes:

1. Scope — a one-paragraph summary of what the PR is (new feature, bug fix, refactor, dep bump, etc.) and what it touches.
2. Blockers — concrete must-fix items. Each blocker has a file path, a line number, and a one-sentence rationale.
3. Nits — nice-to-haves and small polish items. Same shape as blockers but lower urgency.
4. Strengths — what the change gets right. Keeps tone constructive and surfaces patterns worth repeating.

The review is breadth over depth: catch the obvious across any language/stack, leave the deep language-specific antipatterns to a richer user-installed PR/code-review skill (or to a code reviewer with full domain context). If you want multi-persona security/SRE/architecture lenses, jig doesn't ship those — install a heavier skill at the user scope and the router will prefer it.

When to use vs. when to defer

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

• Any other user-installed PR/code-review skill. Common location: ~/.claude/skills/pr-review/ — but the deferral is category-based, not name-based, so a skill named anything (pr-review, code-reviewer, team-pr, etc.) whose description claims PR review, code review, or diff review will be preferred. If one is present, defer to it. The Claude Code skill router should route to the more specific skill automatically; if you want to be sure, explicitly invoke it. The one exception jig's description carves out is the bundled review skill — jig:pr-review does not defer to that one (it's the generic fallback below jig's baseline, not above it).
• /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's a spec-shape review against a written spec. This skill is a PR-shape review against a diff. 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's a PR/diff/branch but no spec to compare against.
• agents/reviewer.md (the reviewer subagent) — different invocation primitive (subagent spawned via Task, not a skill). The subagent runs read-only and produces a structured verdict against a spec. Conceptually in the same neighborhood as /jig:independent-review (which builds the prompt the subagent reads), but distinct from this skill's PR-shape review.

Rule of thumb: spec exists → /jig:independent-review or the subagent. Just a diff → this skill (or the richer user one).

Inputs

Three input modes, ordered by richness:

1. Full repo context (preferred). You're inside a Claude Code session with the repo open. Run git diff main...HEAD (or the appropriate base) to get the diff. You can cross-reference the rest of the repo to check for duplicated logic, follow renames, examine related files, and verify that new code follows existing patterns. Highest signal.

2. land.py prepare --mode pr output (the artifact slice 007-01 ships). When /jig:slice-land has run in pr mode, you get a PR body file and the branch name on disk. Read the PR body for stated intent and the diff for the actual changes. Still has repo context because you're inside the same session.

3. Pasted diff or uploaded files. No repo context. You can review shape, but you cannot verify whether similar logic exists elsewhere in the repo or whether the new code follows local conventions. Call out the limitations in the review header.

Not supported by this baseline: GitHub-PR-URL-only input (no local repo, no MCP integration). Out of scope per spec 012's "GitHub MCP integration deferred" decision. If the user has only a URL, ask them to either open the repo locally or paste the diff. A richer user-installed pr-review skill may handle URL-only input — defer to it if so.

Scope discipline

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

• Different repo / system required (worker, client SDK, infra, upstream spec): drop entirely or mention once in Scope as an "adjacent concern noted" — do NOT promote to Blocker or Nit.
• Amendment to a parent spec, ADR, or design doc: the spec is a contract for this PR, not a checklist to expand. Not a finding here.
• "The PR should also document / specify / add X" where X is a separate concern: separate PR, not a finding here.

Prophylactic expansion — demanding the author address 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 PR, emit a markdown report with exactly these four H2 sections:

## Scope
<one paragraph: what the PR is, what it touches, what it does not touch>

## Blockers
- `path/to/file.py:42` — <one-sentence rationale>. Required because <why>.
- (or: "None.")

## Nits
- `path/to/file.py:7` — <one-sentence rationale>. Nice-to-have because <why>.
- (or: "None.")

## Strengths
- <pattern or choice that's well done>. Worth repeating because <why>.

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

Worked example

Suppose the diff is:

+ def calculate_total(items):
+     total = 0
+     for item in items:
+         total += item.price * item.quantity
+     return total
+
+ def apply_discount(total, code):
+     if code == "SAVE10":
+         return total * 0.9
+     return total

A baseline review would read:

## Scope
Adds two helper functions to the cart module: `calculate_total` and
`apply_discount`. Pure compute, no I/O, no side effects. Touches one
file; no tests added in this diff.

## Blockers
- `cart.py:8` — `apply_discount` has no test coverage and the magic code
  `"SAVE10"` is hard-coded. Required because pricing logic is a common
  source of regressions, and a future code change here would silently
  break the discount.

## Nits
- `cart.py:1` — `calculate_total` does no validation on `item.price` or
  `item.quantity` (e.g., negative quantities). Nice-to-have because the
  caller may or may not guarantee non-negative inputs.

## Strengths
- The two functions are pure and tiny — easy to test, easy to reason
  about. Worth repeating because most cart bugs come from mixing pricing
  logic with persistence.

Notice: no language-specific deep dive (no "use Decimal instead of float for currency", no "this should be a @dataclass"). That depth belongs in a richer user-installed PR/code-review skill, not the baseline.

Gotchas

• A configured review.pr_review_skill (scaffold.json) is honored only in the orchestrated craft pass, not here. Spec 096-01 / ADR-0040 D1 lets a project name its richer PR-review skill in scaffold.json; that key is read by review.py when it builds the craft pass prompt for the spec-workflow reviewer subagent. It is not consulted on this router-only interactive invocation, nor in bug-fix's craft pass. Config honoring on those 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 the Claude Code router "prefer any other installed skill whose description identifies it as handling PR/code/diff review." There is no filesystem probe, no plugin-precedence lookup, no name-matching against pr-review specifically. The deferral is category-based: a user skill named anything that claims the PR/code review surface area will win. If the router consistently picks jig's baseline over such a skill, jig's description is too greedy — open an issue. This router-based deferral applies to interactive use only. The spec-workflow craft pass spawns a read-only reviewer subagent with no Skill tool, so it cannot use the router at all — there review.py does explicit file-read dispatch (detects ~/.claude/skills/pr-review/ and points the reviewer at it). See docs/workflow.md § Post-implementation review.
• 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 PR/code review category wins over jig.
• Lightweight is a feature, not a limitation. The baseline does not ship language-specific reference files (Node, Java, Python, etc.). It does not run multiple personas. It does not check for security issues beyond the obvious. 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 ~/.claude/skills/pr-review/).
• This is a PR-shape review, not a spec-shape review. If a slice has a spec.md to evaluate against, use /jig:independent-review (or spawn the agents/reviewer.md subagent). Mixing the two surfaces leads to reviews that complain about ACs the diff isn't claiming to satisfy.
• Fallback mode (if the routing-dogfood in spec 012-01's DoD ever fails): the SKILL.md frontmatter gets disable-model-invocation: true and this skill becomes explicit-invocation-only (/jig:pr-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, that's why.

Relationship to other skills

• /jig:slice-land — emits the PR-shaped artifact this skill reviews (when run in --mode pr). The two skills compose: slice-land prepares the PR, pr-review evaluates the diff.
• /jig:independent-review — sibling skill, different shape. spec-compliance review against spec.md, not diff review. See "When to use vs. when to defer" above.
• /jig:contracts — orthogonal. Deliberate stub today (ADR-0002); if and when it activates, it will surface module-boundary violations that pr-review could call out as blockers.