Conciseness

Nearly all guidance is delivered via dense tables (model-by-data selection, null-model meanings, score thresholds) with zero filler; no background concepts Claude already knows are re-explained. The gotcha "Scale mismatch — convert first (Step 0)" cross-references instead of repeating. Every section earns its tokens, matching the lean anchor.

Actionability

A copy-paste-ready `tu run DrugSynergy_calculate_bliss` invocation with expected output ("expected 0.58, bliss_synergy_score 0.12") demonstrates the call pattern, and the Step 0 table supplies the exact tool name and input parameter names for all five tools, making every command fully constructible. Concrete numeric interpretation thresholds (>+10 synergy, CI<1) and a real helper script (`scripts/synergy_reference.py`, present in the bundle) complete it.

Workflow Clarity

Steps 0–4 form a clear, data-driven decision sequence with the scale-conversion checkpoint ("inhibition = 1 − viability/100") and anticipated failure modes ("or the Hill fit fails (the tools say so)"). It falls just short of the level-5 anchor because there is no explicit post-run validation/feedback loop (e.g., sanity-check the computed score against the expected range before reporting), and it is above level 3 since checkpoints like the scale-consistency check are explicit rather than implicit.

Progressive Disclosure

The SKILL.md is a well-organized, self-contained overview whose only bundle file — `scripts/synergy_reference.py` — is real, clearly signaled, and one level deep. No content that belongs in a separate file is inlined, and the Related-skills section aids navigation without nesting.

Specificity

The description enumerates five concrete, named reference models ("Bliss independence, HSA / highest single agent, Loewe additivity, ZIP, and the Chou-Talalay Combination Index") and states three concrete deliverables — quantify synergy/additivity/antagonism, explain which model to use and what data each needs, and how to read the score. This matches the anchor for multiple specific concrete actions with comprehensive coverage; it is above the level-4 anchor only in that it has no coverage gaps.

Completeness

Both halves are explicit: the "what" ("quantify whether two drugs together are synergistic, additive, or antagonistic using the standard reference models...") and the "when" ("Use when you have measured single-drug and combination effects (inhibition/viability) and need a synergy score"). This mirrors the anchor-5 example structure of concrete what plus explicit trigger clause; level 4 would require a vaguer 'when'.

Trigger Term Quality

Natural user phrasing is comprehensively covered: "drug combination", "synergy"/"synergistic", "additive", "antagonistic", "synergy score", "single-drug and combination effects", "inhibition/viability". These are the exact words a researcher would use when asking for this skill; no natural synonym class is missing (file extensions are inapplicable here).

Distinctiveness Conflict Risk

A clear niche (computing synergy from measured effects) with an explicit negative boundary — "NOT for looking up pre-computed synergy in a database (use the SYNERGxDB tool / cell-line-profiling skill)" — actively routes away the nearest conflicting use case. This is stronger than the level-4 anchor, which only has minor overlap risk without such routing.