Claude skills for Code Review, tested
Skills for code review work, measured on code review tasks. Each was run on the same task pairs with the skill loaded and without it, and what is below is what changed. Ranked by how many models the rule found a clear effect on, never by the size of one.
Measured on 2 models (GPT & Gemini): GPT-5 mini, Gemini 3.1 Flash Lite.
10 fixture source files in 4 languages, each seeded with known bugs, security issues and correctness problems, 54 in total, drawn from a closed list of 18 defect types that both arms are given. The model is asked to name the symbol each defect sits on, never a line number; the score is the share of seeded defects it names. 50 are verified in the fixtures by mechanical check, 4 are judgement items listed as such, and 30 pieces of correct code that read as suspicious are recorded as traps and are deliberately not in the key.
On the models tested, no skill measurably helped with code review tasks; the unaided scores are the story.
| Task set | Unaided score |
|---|---|
| Code review | 64% |
| Code review | 63% |
| Code review | 63% |
| Code review | 64% |
| Code review | 63% |
| Code review | 64% |
| Code review | 63% |
| Code review | 64% |
The numbers
How to read these tables
How to read these tables
- Without -> with
- The score on the task set with no skill loaded, then with the skill loaded. For classes scored against an answer key, this is the share of seeded items found. For classes scored by blind comparison, it is how often a grader preferred the skill's output over the baseline's, with the baseline shown as the complement.
- Effect (range)
- With minus without, averaged over the models tested, with the lowest and highest per-model value in brackets. Per-model intervals are on each skill's page.
- Orbit
- Stable: delta at or above the pass threshold, and the interval excludes zero
- Past the horizon: delta at or below the failure floor, and the interval excludes zero
- In free drift: the interval spans zero, or the delta sits between the floor and the threshold
- Unobservable: the cell cannot be classified: sub-case (a) an unbounded scale, or sub-case (b) both arms at the same bound
A fifth value, Decaying, is defined and appears once a skill has been re-tested: a cell previously Stable that has fallen below the pass threshold on a later run.
- Cohort
- The repository that publishes the skill. Rows marked with an asterisk come from the repository the operator of this site maintains, so those are the operator measuring its own work. The rest were chosen by a stated rule and not by preference.
- Commit
- The exact version tested. Later commits are not covered by this verdict.
- Injected context tokens
- How much text the skill adds to the model's context. This is cost, not quality; a bigger number is not a better one. Measured from the input tokens the API reported on the with arm, averaged over that skill's records.
- Tested
- The date. Verdicts age as models change.
Code review
| Skill | Cohort | Without -> with | Effect (range) | Orbit | Injected context tokens | Tested |
|---|---|---|---|---|---|---|
| No skill loaded | baseline | 64% | 0 by definition | 0 | 2026-09-05 | |
| One-line instruction instead | baseline | 65% | 0 by definition | 0 | 2026-09-05 | |
plugins/developer-essentials/skills/code-review-excellence from wshobson/agents 38e19c20d2b1 Best result in this test | wshobson/agents | 64% -> 63% | +0.01 [+0.01, +0.02] | In free drift | 3,938 | 2026-09-05 |
skills/code-reviewer from Jeffallan/claude-skills 882ef55e377d | Jeffallan/claude-skills | 63% -> 64% | -0.00 [-0.05, +0.05] | In free drift | 8,290 | 2026-09-05 |
engineering/skills/pr-review-expert from alirezarezvani/claude-skills 19392f7a0826 | alirezarezvani/claude-skills | 63% -> 60% | -0.05 [-0.08, -0.01] | In free drift | 4,260 | 2026-09-05 |
skills/code-review-and-quality from addyosmani/agent-skills d2c37ef6225d | addyosmani/agent-skills | 64% -> 61% | -0.05 [-0.05, -0.04] | In free drift | 5,218 | 2026-09-05 |
skills/gsd-code-review from open-gsd/gsd-core 6beaa66b2587 | open-gsd/gsd-core | 63% -> 59% | -0.05 [-0.07, -0.03] | In free drift | 1,420 | 2026-09-05 |
skills/code-review-web from rampstackco/claude-skills a67dd34c609f | rampstackco/claude-skills* | 64% -> 58% | -0.07 [-0.14, -0.01] | In free drift | 8,206 | 2026-09-05 |
skills/engineering/code-review from mattpocock/skills 6654f6b60cd9 | mattpocock/skills | 63% -> 57% | -0.12 [-0.14, -0.10] | In free drift | 2,278 | 2026-09-05 |
skills/ce-code-review from EveryInc/compound-engineering-plugin c9c10f8c7541 | EveryInc/compound-engineering-plugin | 64% -> 34% | -0.30 [-0.59, -0.02] | Mixed, see page | 73,715 | 2026-09-05 |
| Averaged over three models; per-model results on each skill's page. Ranked within this class only. | ||||||
Ranked within this topic by how many models the rule found a clear effect on, which is a count of verdicts and never the size of one. Two classes are two answer keys on two scales, so no effect here is compared with another. Every class, with its full table.