Code Review Cc

/code-review-cc → scope the diff → per-angle Find → Verify → (Sweep) → ranked findings

Review the current diff for correctness bugs and reuse / simplification / efficiency cleanups. Unlike /simplify-code (quality only), this hunts for bugs too.

Selecting the review

Parse the argument string ($ARGUMENTS):

• Effort level — the first token, one of low · medium · high ·

xhigh · max. If no level is given, default to medium. Higher levels trade precision for recall: low/medium surface fewer, high-confidence findings; high→max widen coverage and may include uncertain findings.

• --fix — after producing the findings list, also apply them (see the

Applying fixes appendix).

• --comment — post findings as inline PR comments (see the *Posting to

GitHub* appendix).

• `` — anything left over (a PR number, branch name, or file path)

is the review target. If a target is given, prepend Review target: \\`` to the run and review that instead of the default diff range.

Follow the single section below that matches the selected effort level.

---

Effort: low

low effort → 1 diff pass → no verify → ≤4 findings

Turn 1 — read

One tool call: read the unified diff (git diff @{upstream}...HEAD; git diff HEAD to cover both committed and uncommitted changes, or git diff main...HEAD / the target passed as an argument). Skip test/fixture hunks (test/, spec/, __tests__/, *_test.*, *.test.*, fixtures/, testdata/) — test-file changes are not reviewed at this level. No subagents, no full-file reads.

Turn 2 — findings

Flag runtime-correctness bugs visible from the hunk alone: inverted/wrong condition, off-by-one, null/undefined deref where adjacent lines show the value can be absent, removed guard, falsy-zero check, missing await, wrong-variable copy-paste, error swallowed in a catch that should propagate. Also flag — still from the hunk alone — new code that duplicates an existing helper visible in the diff context, and dead code the diff leaves behind.

Do not flag style, naming, perf, missing tests, or anything outside the hunk.

Output at most 4 findings, most-severe first, one line each: path/to/file.ext:123 — what's wrong and the concrete failure. If nothing qualifies, output exactly (none).

---

Effort: medium

medium effort → 3+5 angles × 6 candidates → 1-vote verify → ≤8 findings

You are reviewing for precision at medium effort: every finding you surface should be one a maintainer would act on.

Phase 0 — Gather the diff

Run git diff @{upstream}...HEAD (or git diff main...HEAD / git diff HEAD~1 if there's no upstream) to get the unified diff under review. If there are uncommitted changes, or the range diff is empty, also run git diff HEAD and include the working-tree changes in scope — the review often runs before the commit. If a PR number, branch name, or file path was passed as an argument, review that target instead. Treat this diff as the review scope.

Phase 1 — Find candidates (3 correctness angles + 3 cleanup angles + 1 altitude angle + 1 conventions angle, up to 6 each)

Run 8 independent finder angles via the Agent tool. Each surfaces up to 6 candidate findings with file, line, a one-line summary, and a concrete failure_scenario.

Angle A — line-by-line diff scan

Read every hunk in the diff, line by line. Then Read the enclosing function for each hunk — bugs in unchanged lines of a touched function are in scope (the PR re-exposes or fails to fix them). For every line ask: what input, state, timing, or platform makes this line wrong? Look for inverted/wrong conditions, off-by-one, null/undefined deref, missing await, falsy-zero checks, wrong-variable copy-paste, error swallowed in catch, unescaped regex metachars.

Angle B — removed-behavior auditor

For every line the diff DELETES or replaces, name the invariant or behavior it enforced, then search the new code for where that invariant is re-established. If you can't find it, that's a candidate: a removed guard, a dropped error path, a narrowed validation, a deleted test that was covering a real case.

Angle C — cross-file tracer

For each function the diff changes, find its callers (Grep for the symbol) and check whether the change breaks any call site: a new precondition, a changed return shape, a new exception, a timing/ordering dependency. Also check callees: does a parallel change in the same PR make a call unsafe?

Reuse

The angles above hunt for bugs; this one and the next two hunt for cleanup in the changed code. Flag new code that re-implements something the codebase already has — Grep shared/utility modules and files adjacent to the change, and name the existing helper to call instead.

Simplification

Flag unnecessary complexity the diff adds: redundant or derivable state, copy-paste with slight variation, deep nesting, dead code left behind. Name the simpler form that does the same job.

Efficiency

Flag wasted work the diff introduces: redundant computation or repeated I/O, independent operations run sequentially, blocking work added to startup or hot paths. Also flag long-lived objects built from closures or captured environments — they keep the entire enclosing scope alive for the object's lifetime (a memory leak when that scope holds large values); prefer a class/struct that copies only the fields it needs. Name the cheaper alternative.

Altitude

Check that each change is implemented at the right depth, not as a fragile bandaid. Special cases layered on shared infrastructure are a sign the fix isn't deep enough — prefer generalizing the underlying mechanism over adding special cases.

Conventions (CLAUDE.md)

Find the CLAUDE.md files that govern the changed code: the user-level ~/.claude/CLAUDE.md, the repo-root CLAUDE.md, plus any CLAUDE.md or CLAUDE.local.md in a directory that is an ancestor of a changed file (a directory's CLAUDE.md only applies to files at or below it). Read each one that exists, then check the diff for clear violations of the rules they state.

Only flag a violation when you can quote the exact rule and the exact line that breaks it — no style preferences, no vague "spirit of the doc" inferences. In the finding, name the CLAUDE.md path and quote the rule so the report can cite it. If no CLAUDE.md applies, return nothing for this angle.

Cleanup, altitude, and conventions candidates use the same file/line/summary shape; in failure_scenario, state the concrete cost (what is duplicated, wasted, harder to maintain, or which CLAUDE.md rule is broken) instead of a crash. Correctness bugs always outrank cleanup, altitude, and conventions findings when the output cap forces a cut.

Pass every candidate with a nameable failure scenario through — finders that silently drop half-believed candidates bypass the verify step and are the dominant cause of misses.

Phase 2 — Verify (1-vote, 3-state)

Dedup candidates that point at the same line/mechanism, keeping the one with the most concrete failure scenario. For each remaining candidate, run one verifier via the Agent tool: give it the diff, the relevant file(s), and the candidate, and have it return exactly one of:

• CONFIRMED — can name the inputs/state that trigger it and the wrong

output or crash. Quote the line.

• PLAUSIBLE — mechanism is real, trigger is uncertain (timing, env,

config). State what would confirm it.

• REFUTED — factually wrong (code doesn't say that) or guarded elsewhere.

Quote the line that proves it.

Keep candidates where the vote is CONFIRMED or PLAUSIBLE.

Output

Return findings as a JSON array of at most 8 objects:

[
  {
    "file": "path/to/file.ext",
    "line": 123,
    "summary": "one-sentence statement of the bug",
    "failure_scenario": "concrete inputs/state → wrong output/crash"
  }
]

Ranked most-severe first. If more than 8 survive, keep the 8 most severe. If nothing survives verification, return [].

---

Effort: high

high effort → 3+5 angles × 6 candidates → 1-vote verify (recall-biased) → ≤10 findings

You are reviewing for recall at high effort: catch every real bug a careful reviewer would catch in one sitting. At this level, catching real bugs matters more than avoiding false positives. Err on the side of surfacing.

Phase 0 — Gather the diff

Run git diff @{upstream}...HEAD (or git diff main...HEAD / git diff HEAD~1 if there's no upstream) to get the unified diff under review. If there are uncommitted changes, or the range diff is empty, also run git diff HEAD and include the working-tree changes in scope — the review often runs before the commit. If a PR number, branch name, or file path was passed as an argument, review that target instead. Treat this diff as the review scope.

Phase 1 — Find candidates (3 correctness angles + 3 cleanup angles + 1 altitude angle + 1 conventions angle, up to 6 each)

Run 8 independent finder angles via the Agent tool. Each surfaces up to 6 candidate findings with file, line, a one-line summary, and a concrete failure_scenario.

Angle A — line-by-line diff scan

Read every hunk in the diff, line by line. Then Read the enclosing function for each hunk — bugs in unchanged lines of a touched function are in scope (the PR re-exposes or fails to fix them). For every line ask: what input, state, timing, or platform makes this line wrong? Look for inverted/wrong conditions, off-by-one, null/undefined deref, missing await, falsy-zero checks, wrong-variable copy-paste, error swallowed in catch, unescaped regex metachars.

Angle B — removed-behavior auditor

For every line the diff DELETES or replaces, name the invariant or behavior it enforced, then search the new code for where that invariant is re-established. If you can't find it, that's a candidate: a removed guard, a dropped error path, a narrowed validation, a deleted test that was covering a real case.

Angle C — cross-file tracer

For each function the diff changes, find its callers (Grep for the symbol) and check whether the change breaks any call site: a new precondition, a changed return shape, a new exception, a timing/ordering dependency. Also check callees: does a parallel change in the same PR make a call unsafe?

Reuse

The angles above hunt for bugs; this one and the next two hunt for cleanup in the changed code. Flag new code that re-implements something the codebase already has — Grep shared/utility modules and files adjacent to the change, and name the existing helper to call instead.

Simplification

Flag unnecessary complexity the diff adds: redundant or derivable state, copy-paste with slight variation, deep nesting, dead code left behind. Name the simpler form that does the same job.

Efficiency

Flag wasted work the diff introduces: redundant computation or repeated I/O, independent operations run sequentially, blocking work added to startup or hot paths. Also flag long-lived objects built from closures or captured environments — they keep the entire enclosing scope alive for the object's lifetime (a memory leak when that scope holds large values); prefer a class/struct that copies only the fields it needs. Name the cheaper alternative.

Altitude

Check that each change is implemented at the right depth, not as a fragile bandaid. Special cases layered on shared infrastructure are a sign the fix isn't deep enough — prefer generalizing the underlying mechanism over adding special cases.

Conventions (CLAUDE.md)

Find the CLAUDE.md files that govern the changed code: the user-level ~/.claude/CLAUDE.md, the repo-root CLAUDE.md, plus any CLAUDE.md or CLAUDE.local.md in a directory that is an ancestor of a changed file (a directory's CLAUDE.md only applies to files at or below it). Read each one that exists, then check the diff for clear violations of the rules they state.

Only flag a violation when you can quote the exact rule and the exact line that breaks it — no style preferences, no vague "spirit of the doc" inferences. In the finding, name the CLAUDE.md path and quote the rule so the report can cite it. If no CLAUDE.md applies, return nothing for this angle.

Cleanup, altitude, and conventions candidates use the same file/line/summary shape; in failure_scenario, state the concrete cost (what is duplicated, wasted, harder to maintain, or which CLAUDE.md rule is broken) instead of a crash. Correctness bugs always outrank cleanup, altitude, and conventions findings when the output cap forces a cut.

Pass every candidate with a nameable failure scenario through — finders that silently drop half-believed candidates bypass the verify step and are the dominant cause of misses.

Phase 2 — Verify (1-vote, recall-biased)

Dedup near-duplicates (same defect, same location, same reason → keep one). For each remaining candidate, run one verifier via the Agent tool: give it the diff, the relevant file(s), and the candidate; it returns exactly one of CONFIRMED / PLAUSIBLE / REFUTED.

PLAUSIBLE by default — do not refute a candidate for being "speculative" or "depends on runtime state" when the state is realistic: concurrency races, nil/undefined on a rare-but-reachable path (error handler, cold cache, missing optional field), falsy-zero treated as missing, off-by-one on a boundary the code does not exclude, retry storms / partial failures, regex/allowlist that lost an anchor. These are PLAUSIBLE.

REFUTED only when constructible from the code: factually wrong (quote the actual line); provably impossible (type/constant/invariant — show it); already handled in this diff (cite the guard); or pure style with no observable effect.

Keep CONFIRMED and PLAUSIBLE. Drop REFUTED.

Output

Return findings as a JSON array of at most 10 objects:

[
  {
    "file": "path/to/file.ext",
    "line": 123,
    "summary": "one-sentence statement of the bug",
    "failure_scenario": "concrete inputs/state → wrong output/crash"
  }
]

Ranked most-severe first. If more than 10 survive, keep the 10 most severe. If nothing survives verification, return [].

---

Effort: xhigh

xhigh effort → 5+5 angles × 8 candidates → 1-vote verify → sweep → ≤15 findings

You are reviewing for recall at extra-high effort: catch every real bug. At this level, catching real bugs matters more than avoiding false positives — a missed bug ships. Err on the side of surfacing.

Phase 0 — Gather the diff

Run git diff @{upstream}...HEAD (or git diff main...HEAD / git diff HEAD~1 if there's no upstream) to get the unified diff under review. If there are uncommitted changes, or the range diff is empty, also run git diff HEAD and include the working-tree changes in scope — the review often runs before the commit. If a PR number, branch name, or file path was passed as an argument, review that target instead. Treat this diff as the review scope.

Phase 1 — Find candidates (5 correctness angles + 3 cleanup angles + 1 altitude angle + 1 conventions angle, up to 8 each)

Run 10 independent finder angles via the Agent tool. Each surfaces up to 8 candidate findings. Do NOT let one angle's conclusions suppress another's — if two angles flag the same line for different reasons, record both.

Angle A — line-by-line diff scan

Read every hunk in the diff, line by line. Then Read the enclosing function for each hunk — bugs in unchanged lines of a touched function are in scope (the PR re-exposes or fails to fix them). For every line ask: what input, state, timing, or platform makes this line wrong? Look for inverted/wrong conditions, off-by-one, null/undefined deref, missing await, falsy-zero checks, wrong-variable copy-paste, error swallowed in catch, unescaped regex metachars.

Angle B — removed-behavior auditor

For every line the diff DELETES or replaces, name the invariant or behavior it enforced, then sear

…

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: extractumio
• Source: extractumio/extractum-skills
• License: MIT

Install and usage instructions live in the source repository linked above.