What are the signs that an agent skill is over-optimised?

Why an agent skill can look better while doing less

An over-optimised skill usually improves the visible shape of the answer before it improves the substance. You may see tighter phrasing, fewer digressions, cleaner bullets, or lower token usage, but the trade-off is that required steps, exceptions, caveats, or edge cases quietly disappear. The result can look disciplined in review while becoming less reliable for real task execution.

That is why transcript review alone is not enough. A compact response is only a win if it still answers the full task, preserves the needed constraints, and does not omit important follow-through. In practice, the signal is not “shorter is worse”, it is “shorter plus missing intent coverage is a regression.”

What the strongest warning signs usually are

The clearest signs show up in the output itself. The skill may start returning answers that are consistently briefer than before, but also less specific, less complete, and more generic. It may over-favour polished formatting, templated language, or concise summaries even when the task requires detail, sequencing, or explicit reasoning.

Another warning sign is that the answer looks successful on surface quality metrics while failing on task fidelity. If the response no longer includes necessary instructions, intermediate reasoning, exceptions, or user constraints, the optimisation has likely shifted from usefulness to style. A skill can also become brittle, where it handles common cases neatly but drops nuance as soon as the prompt is slightly unusual.

A useful internal check is whether the skill is optimising for presentation artefacts rather than outcome quality. Lower tokens, cleaner headings, and more direct language are all fine until they start correlating with lost coverage. When that happens, the apparent efficiency is masking an execution gap.

How to test for over-optimisation without being fooled by polish

The best test is to compare output quality against a task-completion rubric, not against appearance alone. Ask whether the skill preserved all required content, handled edge cases, and kept the answer actionable. If the polished version cannot be relied on to satisfy the original request, the optimisation has gone too far.

It also helps to test the same skill against prompts of varying complexity. Over-optimised skills often do fine on short, obvious tasks but lose ground when the request needs layered judgment or multiple constraints. If the response quality degrades as soon as the task is less “template-friendly”, that is a sign the skill has learned to compress too aggressively.

• Check for missing requirements, not just awkward phrasing.
• Compare coverage of key points before and after the change.
• Look for cleaner outputs that still fail on completeness.
• Use harder prompts to see whether nuance survives.

Risk and Threat Considerations

Over-optimised agent skill create a quiet reliability risk because the failure mode is attractive output that omits material content. In operational settings, that can lead teams to trust a skill that is fast and readable but systematically under-delivers on completeness, especially when reviewers skim rather than verify against requirements.

Failure mechanism: optimisation pressure rewards brevity, formatting consistency, or lower token use more than answer coverage, so the skill learns to prune content that looks optional but is actually required for task success.

Impact: users may accept incomplete or misleading outputs, miss edge cases, or make downstream decisions on a partial answer that appears more confident and polished than it really is.

Practitioner Guidance

What to verify: Before treating a skill improvement as real, verify that the “better” output still satisfies a completeness checklist for the task type. The right question is not whether the response is cleaner, but whether anything essential was removed in the process.

What good looks like: A well-tuned skill should reduce noise without dropping requirements, constraints, or decision-critical detail. If readability improves and coverage stays stable, the optimisation is likely healthy; if readability improves while coverage falls, it is overfitted to style.

Practitioner takeaway: Treat brevity as a benefit only when it is accompanied by preserved task fidelity, because polish without completeness is a reliability regression, not an improvement.

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