REVIEW 4 major objections 6 minor 26 references
Skill-Use: Can LLMs Actually Use Skills in Agentic Harnesses?
T0 review · 4 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read Skill-Use: LLM agents cannot yet reliably use skills, topping out at 0.613 on a new benchmark.
desk verdict A genuinely useful benchmark with a headline number that does not survive its own measurement noise, while the qualitative findings do. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the SKILL-USE benchmark itself, built around the progressive-disclosure protocol: the agent sees only the skill's name, one-line description, and file path, and must open the skill file to obtain the full procedure. The scoring formula is a gated aggregate, SU(y)=g(y;s)[αC(y)+(1−α)B(y)], where g is the Trigger indicator, C is weighted Compliance over prescribed requirements, B is weighted Boundary over prohibitions, and α=0.7. The rubric items are trajectory-derived: deterministic checks on tool calls and artifact states where possible, and a scope-restricted LLM judge that scores one item at a time with double scoring and one re-adjudication elsewhere. This machinery is what lets the paper attribute failures to recognition, execution, or restraint separately, and it is what grounds the claim that execution credit should only count after a trigger.
What would settle it
Rescore all 177 SKILL-USE trajectories with human expert annotators and compare the resulting model rankings with the LLM-judge rankings; if any tier-level ordering changes, the paper's ranking claims fail. Separately, re-running the same eight models under the same two harnesses on a fresh set of community skills would test whether the 79-skill sample, not the measured capability, drives the results.
Extended reading notes
Core claim
The central discovery is that reliable skill use under progressive disclosure is out of reach for the current generation of LLM agents, and that the failure is not a single bottleneck. SKILL-USE separates Trigger (does the agent retrieve the relevant skill from its name and short description alone), Compliance (does it follow the prescribed procedure), and Boundary (does it avoid forbidden operations), and combines them into a gated Skill-Use score that credits execution only after triggering. The strongest configuration on the benchmark is GPT-5.5 under the Claude Code harness with an SU of 0.613; even among triggered traces, no model exceeds 0.638 Compliance. Boundary is consistently higher than Compliance, so avoiding prohibited actions is easier than completing a full prescribed workflow. Preloading the full skill document mostly raises Trigger and barely changes execution, which identifies retrieval as the main gap, and the per-model cross-harness correlations show that skill use behaves as a capability conditioned on the harness rather than a fixed property of the model.
Load-bearing premise
The load-bearing premise is that the automated judge's rubric scores, whose agreement when the same traces are rescored is only moderate, are accurate enough to rank models and that the 79 curated skills stand in for real-world skill use.
Editorial extensions
If this is right
- Even when a model does retrieve the skill, faithful execution is not guaranteed: the best conditional Compliance is 0.638.
- Showing the full skill text instead of the name-and-description entry point mainly lifts Trigger; post-trigger execution is barely affected, so retrieval is the dominant bottleneck under native injection.
- Growing the skill library from one to ten skills causes most of the Trigger drop, driven by runs that call no skill rather than by selecting a wrong one.
- Within-scope skill use and out-of-scope restraint are negatively rank-correlated, so a model that follows skills well can also be the most likely to over-invoke them.
- Adding a skill library is not automatically beneficial: paired task completion rises above the no-skill baseline only when SU exceeds about 0.5.
Reading between the lines
- Editorial inference: if skill use is harness-conditioned, benchmark reports should always state the harness and report per-harness leaderboards, because a single model ranking without the harness will mislead.
- Editorial inference: the moderate ICC(2,1)=0.530 of repeated LLM-judge scoring suggests per-item rubric verdicts carry noticeable noise; a human rescoring of the 177 tasks with expert annotators would tell whether the tier-level rankings survive.
- Editorial inference: a testable extension would vary distractor skill descriptions for a fixed library size to see whether Trigger failures track description ambiguity rather than library size.
- Editorial inference: since preloading barely changes post-trigger execution, training that targets skill selection may yield larger SU gains than training that targets procedure following; this is a prediction, not a benchmark result.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces Skill-Use, a benchmark that evaluates whether LLM agents can use skills under progressive disclosure, where an agent sees only a skill's name and short description and must retrieve the full procedure. Skill-Use decomposes skill use into Trigger, Compliance, and Boundary, and combines them into a gated SU score. The benchmark contains 79 real skills, 177 executable tasks, and 1,314 rubric items, and is validated with Docker sandboxes, masked-skill checks, multi-family adversarial review, human audit, and rescoring experiments. The evaluation of eight LLMs under two harnesses (Claude Code and Codex) finds that the strongest configuration reaches SU 0.613, that Trigger and Compliance are independent bottlenecks, and that scores and rankings shift with the harness.
Significance. If the results hold, Skill-Use fills a genuine gap: existing skill benchmarks either preload the full skill or measure task success, and instruction-following benchmarks place constraints directly in the prompt. The construction pipeline is unusually careful: deterministic verifiers, isolated execution, multi-family adversarial review, a human audit with 86/100 pairwise agreement, and repeated rescoring are all strengths. The paired experiments on skill injection, library size, out-of-scope avoidance, and task-completion gain are well designed and go beyond a leaderboard. The cross-harness result is the most robust finding: per-model shifts such as Kimi-K2.6 +0.185 and GPT-5.5 -0.110 in Table 6 are many times larger than the reported scoring noise, so the claim that skill use is conditioned on the harness is credible. The main risks are the moderate reliability of the LLM judge, the lack of uncertainty intervals on the headline numeric claim, and the model-dependence of the skill-exclusivity filter; these are fixable in revision.
major comments (4)
- [§4.2, Table 1; Appendix E.5, Table 10] The claim that GPT-5.5 under CC is the strongest configuration, with SU 0.613, is not supported by the reported measurement precision. The rescore study reports ICC(2,1)=0.530 and a within-observation standard deviation of 0.141 for Skill-Use. With roughly 177 tasks per model, the standard error of a model mean is about 0.011, so the gaps to Claude Opus 4.7 (0.599) and Claude Opus 4.8 (0.597) are only about 1.3-1.5 standard errors; for a paired difference the gap is even less than one standard error. The manuscript should either report bootstrap confidence intervals for model means and differences or rephrase the abstract and Section 4.2 to state the top SU as a range (e.g., about 0.60-0.61). The qualitative conclusion that reliable skill use is out of reach is not affected, nor are the large harness-induced shifts, but the specific 'strongest configuration' wording is currently unwarranted. Appendix E.5 states that Section 4.2 makes no ordering claim between adjacent mid-range models; this contradicts the abstract and the main text, which do name GPT-5.5 under CC as the strongest configuration.
- [Appendix E.5, Table 10; §4.3, Figure 3] The Boundary component has low reliability: ICC(2,1)=0.471 with only 39 observations, and the within-observation standard deviation is 0.186. Section 4.2 uses Boundary to claim that boundary adherence exceeds compliance across all model-harness configurations, and Section 4.3 builds on category-level Boundary scores, including the Security & Compliance exception in Figure 3. With 39 boundary observations, category-level Boundary scores for categories such as Security (8 skills, 15 tasks) may carry large uncertainties, and the claim that Security & Compliance is the sole category where Boundary falls below Compliance needs a confidence interval or, at minimum, a statement of the number of boundary items contributing to that category. Please report per-category uncertainty or aggregate over multiple scoring passes before making the exception claim.
- [§3.3, Appendices B.2, B.4] The skill-exclusivity filter is model-dependent, and the manuscript does not report which models performed the masked-skill check and the adversarial review. The masked-skill check removes any requirement that a 'strong model' meets from the prompt alone, and the adversarial review requires agreement among reviewers from 'different model families'; the evaluated models come from overlapping families. This makes 'skill-exclusive' an agreement among the construction models, which the paper itself acknowledges, but the consequence is that the benchmark could partly measure whether an evaluated model's blind spots coincide with the construction models' blind spots. This is a correctness-risk concern, not a dismissal: the operational definition is reasonable, but it needs a concrete validation. Please (a) state which model families and versions executed the masked-skill check and the adversarial review, (b) rerun the masked-skill check with a held-out frontier family and report the proportion of retained requirements that it passes from the prompt alone, and (c) report the human-audit flags from Appendix C on items that annotators judged as satisfiable without the skill; currently Appendix C reports only rubric-satisfaction agreement, not the exclusivity flags.
- [§3.1, Definition 1; Appendix D] The definition of Trigger, I[Retrieve(s)∈τ], leaves unspecified what counts as a retrieval event in each harness. The paper notes that CC has a Skill() step that Codex lacks, and the turn limits differ (120 vs. 80), but it does not state whether a Skill() tool invocation automatically loads the full procedure or whether the model must explicitly open the skill file. If Skill() automatically loads the document, then Trigger under CC measures a different decision than a file-open under Codex, which could affect the cross-harness comparison and the claim that retrieval is the main bottleneck. Please specify the retrieval event for each harness and confirm that the trigger gate is defined identically across harnesses.
minor comments (6)
- [Table 1] The table reports an 'SU+' column that is never defined in the main text or the caption; the caption defines Compliance† and Boundary† but not SU+. Please define SU+ explicitly as the SU score restricted to triggered traces, or rename it for clarity.
- [Appendix C] The human audit would be more informative if it reported the number of rubric items that annotators flagged as satisfiable without the skill, since that is the direct human check on the masked-skill filter; the current report of 86/100 pairwise agreement measures only rubric-satisfaction agreement.
- [§4.5, Appendix E.3] There is an internal inconsistency: Section 4.5 says the library-size experiment runs under CC, but Appendix E.3 explains Qwen3.6-Max's 'none' outcomes as being cut off by the 80-turn Codex limit. Since CC has a 120-turn limit, this should be resolved or corrected.
- [Figure 10] The labels in Figure 10 appear as corrupted unicode tokens (e.g., '/uni00000012') in the current version, making the figure unreadable; please regenerate the figure with proper text rendering.
- [§4.5] The library-size experiment uses randomly sampled distractors, but the text and figures do not report variance across distractor samples or whether the sampling was repeated; please state whether the plotted curves are single draws or averages over multiple random seeds.
- [Abstract and §4.2] The term 'reliable skill use' is used without a threshold; please define what SU value would count as reliable, or replace the phrase with a quantitative statement such as 'no configuration exceeds SU 0.65' to make the claim falsifiable.
Circularity Check
No significant circularity: Skill-Use scores are direct rubric measurements, and the benchmark's construction choices do not feed back as fitted parameters; the concern about the named strongest configuration is a measurement-precision issue, not circularity.
full rationale
The derivation chain in this paper is definitional and measurement-based. SU is defined directly by Eq. 2 as g[αC + (1−α)B] with a deterministic Trigger gate and a fixed α=0.7; Compliance and Boundary are weighted averages of per-item rubric verdicts. All headline findings (e.g., strongest SU 0.613, harness shifts in Table 6, preloading effects in Figures 4–5) are reported means over logged trajectories, not outputs fitted from a parameterized model. The masked-skill check and multi-agent adversarial review (Appendices B.1–B.4) select and validate benchmark instances using LLM judgments, and the evaluated models come from overlapping families; B.4 even says 'Exclusivity is thus an agreement among models, not one author's claim.' This is a construct-validity limitation, but it is not circularity: the LLM judgments determine which items enter the benchmark, not the SU value a model receives, and the human audit in Appendix C (86/100 agreement, κ=0.65) provides an independent check on the rubrics. References [17] and [18] on harness effects are external works, not self-citations, and no load-bearing mathematical claim is imported from prior work by these authors. One non-circular correctness concern: Appendix E.5 reports ICC(2,1)=0.530 with within-observation std 0.141 for Skill-Use, while Section 4.2 names GPT-5.5 under CC (SU 0.613) as the strongest configuration ahead of Claude Opus 4.7 (0.599) and Claude Opus 4.8 (0.597); that gap is within judge-noise range. This is a statistical-claim issue, not a reduction of the result to its inputs, so it does not raise the circularity score.
Assumptions & free parameters
free parameters (3)
- alpha (compliance weight) =
0.7
- Skill selection thresholds (tau_den, tau_sty, tier requirements) =
tau_den=0.30, tau_sty=0.25, tier A/B/C rules
- Turn and wall-clock limits =
120 turns CC, 80 turns Codex, 1,500s
assumptions (3)
- domain assumption Golden trajectories or reference implementations do not leak into retrieval
- domain assumption The checklist in the human audit and the GPT-5.4 judge capture all evaluable skill requirements
- domain assumption Physical file operations and tool calls are the only behavioral traces that matter
invented entities (2)
-
The Skill-Use benchmark itself (79 skills, 177 tasks, 1,314 rubric items)
independent evidence
-
The Skill-Use (SU) score gating formula, Eq. 2
Cite this review
Pith. "Pith review of Skill-Use: Can LLMs Actually Use Skills in Agentic Harnesses?." pith.science (2026). https://pith.science/paper/6PWYHHGL
@misc{pith2026260804828,
author = {Pith},
title = {Pith review of: Skill-Use: Can LLMs Actually Use Skills in Agentic Harnesses?},
year = {2026},
howpublished = {\url{https://pith.science/paper/6PWYHHGL}},
note = {Machine review of arXiv:2608.04828}
}
read the original abstract
Large language model (LLM) agents increasingly rely on skills, structured documents that specify when to act, which procedure to follow, and which tools are allowed. Existing evaluations mostly judge the quality of a skill or its contribution to task success, leaving unexamined whether an agent can recognize a relevant skill and apply it on its own. We introduce Skill-Use, a benchmark that evaluates skill use under progressive disclosure, where an agent sees only a skill's name and short description and must retrieve the full procedure before following it. Skill-Use separates three facets of skill use. Trigger measures whether the agent invokes the relevant skill, Compliance measures how faithfully it follows the prescribed procedure, and Boundary measures whether it avoids forbidden operations. A Skill-Use (SU) score combines the three and credits execution only after the skill is triggered. Skill-Use pairs 79 real skills with 177 executable tasks across nine domains, each grounded in real files, run in an isolated Docker sandbox, and scored by a trajectory-based rubric. Evaluating eight LLMs under two agent harnesses, we find that reliable skill use remains out of reach, as the strongest configuration reaches an SU of only 0.613. Triggering and procedural compliance fail as independent bottlenecks, and both scores and model rankings shift with the harness, so skill use behaves as a capability conditioned on the harness rather than a fixed property of the model.
Figures
Figures from the paper (17 more)
Reference graph
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Fetch under quota1,500 1,000fetch failure
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Rule scoring1,000 400generic, no rule
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pdftk-server
Masked-skill eval400 80–150no exclusive rule Table 3:Skill selection funnel.Input and output counts (approximate) and dominant rejection reason for each of the four phases that reduce 105,586 candidate GitHub skills to 79. Phase 1 output is downsampled to the Phase 2 fetch quo...
Reviewed August 6, 2026 · model on record in the stance chip above.
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