Adding more instructions can make an agent worse. The useful question is whether a reusable skill helps the same model solve the same task; paired evaluation separates that contribution from improvements caused by a stronger model or a different execution harness.
Key Findings
- The June 2026 revision evaluates 87 tasks across eight domains and 18 model–harness configurations. Expert-curated skills increase average pass rate from 33.9% to 50.5%, a gain of 16.6 percentage points.
- Gains vary from 4.1 to 25.7 percentage points across configurations. A skill library therefore needs evaluation with the agent stack that will actually use it.
- Packages with at most three modules outperform larger bundles; compact procedural guidance can be more useful than exhaustive reference material.
- Some smaller models with skills match larger models without them, making skill quality relevant to model selection as well as prompt design.
Who Should Read It
Useful for developers deciding how to package, test, and maintain agent expertise. Deterministic checks and controlled comparisons offer a practical evaluation pattern. The curated tasks do not establish that any community skill will help: validate your own workflows, and measure regressions alongside average gains.