SkillCoach: Self-Evolving Rubrics for Evaluating and Enhancing Agentic Skill-Use
Pith reviewed 2026-07-03 14:16 UTC · model grok-4.3
The pith
SkillCoach derives self-evolving rubrics from rollouts to evaluate agent skill-use on process dimensions distinct from final success.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
SkillCoach derives skill-grounded process rubrics from real rollouts and evaluates trajectories along four dimensions: skill selection, skill following, skill composition, and skill-grounded reflection. It keeps the external verifier as a separate outcome signal, allowing process quality to be distinguished from accidental task success. The evolved rubrics further serve as process supervision for selecting high-quality training trajectories.
What carries the argument
Self-evolving rubrics derived from rollouts that score trajectories on four process dimensions and supply process supervision signals separate from outcome verification.
If this is right
- Evolved rubrics substantially improve evaluation quality over final accuracy alone.
- They expose failures hidden by final accuracy.
- They provide stronger supervision signals than outcome-only filtering for selecting training trajectories.
- Process quality can be tracked independently of whether the task succeeds by chance.
Where Pith is reading between the lines
- The separation of process and outcome signals could apply to other agent evaluation settings that currently rely only on end results.
- Self-evolution of rubrics might reduce the need for manual rubric design when new skills or domains appear.
- Using process rubrics for filtering could produce training data that leads to agents less prone to trial-and-error behavior in multi-skill environments.
Load-bearing premise
Rubrics automatically derived from rollouts capture meaningful distinctions in the four process dimensions without systematic bias from the initial rollout distribution or the evolution process.
What would settle it
A side-by-side rating of the same trajectories by human experts where the evolved rubrics show no higher agreement with the experts than final accuracy alone does.
read the original abstract
Skills are becoming a reusable operational layer for LLM agents, encoding SOPs, domain rules, tool workflows, scripts, and validation routines. In realistic skill repositories, overlapping skills make reliable skill-use difficult. Final verifier success is too coarse for both evaluation and training, since an agent may pass through trial and error while selecting distractor skills, skipping required steps, composing workflows incorrectly or omitting final checks. We introduce SkillCoach, a self-evolving rubric framework for evaluating and enhancing agentic skill-use. SkillCoach derives skill-grounded process rubrics from real rollouts and evaluates trajectories along four dimensions: skill selection, skill following, skill composition, and skill-grounded reflection. It keeps the external verifier as a separate outcome signal, allowing process quality to be distinguished from accidental task success. The evolved rubrics further serve as process supervision for selecting high-quality training trajectories. Experiments show that evolved rubrics substantially improve evaluation quality, expose failures hidden by final accuracy, and provide stronger supervision signals than outcome-only filtering for enhancing agentic skill-use.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript introduces SkillCoach, a self-evolving rubric framework for evaluating and enhancing agentic skill-use in LLM agents. It derives skill-grounded process rubrics from real rollouts and evaluates trajectories along four dimensions: skill selection, skill following, skill composition, and skill-grounded reflection. The external verifier is kept separate as an outcome signal. Experiments demonstrate that the evolved rubrics improve evaluation quality, expose failures hidden by final accuracy, and provide stronger supervision signals than outcome-only filtering.
Significance. If the results hold, SkillCoach could offer a valuable method for process-level evaluation and supervision in agentic systems, addressing the limitations of coarse final verifiers in environments with overlapping skills. The explicit separation of process and outcome signals is a positive design choice that allows distinguishing genuine skill-use quality from accidental success.
major comments (2)
- [Experiments] The central claim that evolved rubrics capture meaningful distinctions in the four process dimensions without systematic bias from the initial rollout distribution requires stronger validation. The manuscript does not provide ablations or analyses showing that the rubric evolution is independent of the base agent's exploration policy or skill repository characteristics, which is load-bearing for the claim that improvements reflect discovery of hidden process failures rather than re-weighting of the original distribution (Experiments section).
- [Method] Details on the self-evolution mechanism for rubrics are insufficient to assess whether criteria remain anchored to independent process quality or propagate skews from the initial trajectories used for both generation and evaluation (Method section).
minor comments (1)
- [Abstract] The abstract could more explicitly state the base models, datasets, or skill repositories used in the experiments to provide context for the claimed improvements.
Simulated Author's Rebuttal
We thank the referee for the detailed and constructive report. The two major comments highlight important areas for strengthening the validation of our claims and the clarity of the method. We address each below and commit to revisions that directly respond to the concerns.
read point-by-point responses
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Referee: [Experiments] The central claim that evolved rubrics capture meaningful distinctions in the four process dimensions without systematic bias from the initial rollout distribution requires stronger validation. The manuscript does not provide ablations or analyses showing that the rubric evolution is independent of the base agent's exploration policy or skill repository characteristics, which is load-bearing for the claim that improvements reflect discovery of hidden process failures rather than re-weighting of the original distribution (Experiments section).
Authors: We agree that demonstrating independence from the initial rollout distribution is important for the central claim. The current experiments compare evolved rubrics against outcome-only baselines and show improved detection of process failures, but they do not include the requested cross-policy or cross-repository ablations. In the revision we will add these analyses: we will re-run rubric evolution using trajectories from two additional base agents with different exploration policies and from a second skill repository, then measure whether the resulting rubrics yield consistent process-quality rankings and supervision gains. This will directly test whether improvements arise from re-weighting the original distribution or from discovery of generalizable process criteria. revision: yes
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Referee: [Method] Details on the self-evolution mechanism for rubrics are insufficient to assess whether criteria remain anchored to independent process quality or propagate skews from the initial trajectories used for both generation and evaluation (Method section).
Authors: We acknowledge that the current Method section provides only a high-level description of the self-evolution loop. In the revision we will expand this section with (1) a detailed algorithm box showing the exact steps of rubric generation, scoring, and iterative refinement, (2) explicit discussion of how the external verifier remains an independent outcome signal that is never used to modify rubric criteria, and (3) concrete examples illustrating how a rubric criterion is updated only when multiple trajectories exhibit the same process pattern, thereby reducing the risk of propagating single-trajectory skews. These additions will allow readers to evaluate whether the mechanism stays anchored to process quality. revision: yes
Circularity Check
No significant circularity; derivation remains self-contained with external verification
full rationale
The paper derives rubrics from rollouts, evolves them, and applies them to distinguish process quality from outcome success while keeping the external verifier separate. Experiments then measure improvements in evaluation quality and supervision signals against baselines. No quoted step reduces a central claim (e.g., 'improved evaluation quality') to a fitted parameter or self-citation by construction; the four process dimensions are evaluated via the evolved rubrics but validated externally rather than tautologically. This is the normal case of an independent experimental pipeline.
Axiom & Free-Parameter Ledger
Reference graph
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[24]
skill_selection (GATE): did the agent select the required gold skill(s) and avoid distractor skills? In a no-gold setting, did it correctly refuse to use a skill? If this fails, downstream dimensions are discounted
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[25]
not needed
skill_following: did the agent actually perform the skill’s KEY STEPS (not just name the skill)? Steps marked "not needed" for this instance do not count against coverage. 17
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[26]
skill_composition_order: for multi-skill / multi-step tasks, are the step ORDER and the passing of intermediate artifacts between skills correct? If the task has a single gold skill this dimension is not_applicable
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[27]
key_steps
result_reflection: before finishing, did the agent do an EXPLICIT, visible self-check / verification / reflection of its result? Only visible behavior counts; never assume hidden reasoning. verifier: the task’s hard verifier result. This is an external outcome signal produced by a rule runner, not an LLM judgment, and it is not part of the process meta sc...
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[28]
Return at least 4 key steps unless the task is truly trivial. 18
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[29]
At least one key step must come from the gold skill content
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[30]
At least one key step must be tied to the final artifact or verifier requirement
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[31]
Every critical step must include positive_evidence and negative_evidence
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[32]
Each description must describe an action that can be checked against tool calls, messages, files, commands, or artifacts
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[33]
rubric_id
Do not infer hidden reasoning. Only visible trajectory evidence counts. Return ONLY the JSON object. USER PROMPT TEMPLATE Extract evidence-checkable key steps for task ‘<task_id>‘. <TASK_INSTRUCTION> <task instruction redacted> </TASK_INSTRUCTION> <FULL_GOLD_SKILL_PACK::<skill_name>> <full gold SKILL.md content redacted> </FULL_GOLD_SKILL_PACK::<skill_nam...
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[34]
skill_selection must name the actual gold skills and distractor skills
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[35]
skill_selection must distinguish real skill use (SKILL.md was read) from merely mentioning a skill name
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[36]
skill_following.key_steps must be exactly the provided EXTRACTED_KEY_STEPS
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[37]
skill_following criteria and score_rules must refer to key step IDs
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[38]
If there is only one gold skill, set skill_composition_order.applicable to false
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[39]
If there are multiple gold skills or ordered substeps, fill expected_order, dependencies, and handoff_requirements
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[40]
result_reflection only counts visible self-checking behavior
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[41]
verifier is not judged by an LLM; it comes from the hard benchmark verifier
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[42]
Launching skill:
Sample real rollouts are only for trajectory format and common mistakes. They are not labels. Return ONLY the JSON rubric. USER PROMPT TEMPLATE Generate the R0 rubric for task ‘<task_id>‘. <TASK_INSTRUCTION> <task instruction redacted> </TASK_INSTRUCTION> <TASK_PACKAGE> <task package JSON redacted> </TASK_PACKAGE> <GOLD_SKILL::<skill_name>> <full gold SKI...
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[43]
correct means all required gold skills were selected and no harmful distractor was used
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[44]
partial means a gold skill was read or invoked, but distractor evidence also appears
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[45]
wrong means the agent mainly selected a distractor or used the wrong skill path
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[46]
missing means no gold skill evidence is found
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[47]
false_trigger is true when the agent uses a skill in a no-gold setting or forces an irrelevant skill
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[48]
dimension
Every positive judgment must cite event_index evidence. INPUT TEMPLATE <EVENT_INDEXED_TIMELINE> <compact timeline with event_index retained> </EVENT_INDEXED_TIMELINE> <SKILL_EVENTS> <skill event JSON, if present> </SKILL_EVENTS> <GOLD_SKILLS> <gold skill names> </GOLD_SKILLS> <DISTRACTOR_SKILLS> <distractor skill names> </DISTRACTOR_SKILLS> Prompt 4: Skil...
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[49]
Do not output critical_step_coverage
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[50]
The code will compute score and coverage later
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[51]
completed and partial require at least one event_index evidence item
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[52]
missing may have empty evidence
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[53]
not_needed must cite the key step’s optional_condition
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[54]
schema_version
If there is no gold skill invocation evidence, do not mark critical skill-specific steps as completed. Return ONLY that JSON object. USER PROMPT TEMPLATE Judge dimension ‘skill_following‘ for a trajectory on task ‘<task_id>‘. <DIMENSION_RUBRIC> <skill_following rubric JSON, including key_steps> </DIMENSION_RUBRIC> <GOLD_SKILLS> <gold skill names> </GOLD_S...
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[55]
First infer observed_order from the trajectory
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[56]
Compare observed_order with expected_order
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[57]
Check whether each dependency’s artifact was produced before it was consumed
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[58]
Check whether handoff_requirements are satisfied
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[59]
If there is only one gold skill and no ordered dependencies, return score 1.0 and order_correct=null
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[60]
dimension
Cite event_index evidence for every error. Return ONLY that JSON object. USER PROMPT TEMPLATE Judge dimension ‘skill_composition_order‘ for a trajectory on task ‘<task_id>‘. <DIMENSION_RUBRIC> <composition rubric JSON with expected_order, dependencies, and handoff requirements> </DIMENSION_RUBRIC> <GOLD_SKILLS> <gold skill names> </GOLD_SKILLS> <DISTRACTO...
discussion (0)
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