Very timely paper. An agent skill can be completely relevant to the task and still make the agent worse.

This study compares the same tasks under different skill setups while keeping the model, agent framework, repository, and verifier fixed.

Across 307 confirmed skill-induced failures, the bigger problem was not obviously irrelevant skills. Among 125 functional failures, 86 came from task-implementation faults: the skill pushed the agent to fill a required element incorrectly or omit it entirely.

Cost failures had a similar pattern. Among 182 high-confidence efficiency regressions, 114 came from extra procedure, not just longer prompts. Excessive verification alone caused 67 cases, with skills turning tests, rebuilds, debugging, and checklists into mandatory work.

The practical warning is simple: a skill can be perfectly on-topic and still make an agent worse.

So for agent platforms, loading a skill should be treated like changing system behavior: check it against task requirements, compare it with a no-skill run, and measure the extra actions it induces.

– arxiv. org/abs/2608.11888

Title: "Agent Skills Can Be Harmful: An Empirical Study of Skill-Induced Failures in LLM Agents"