Conciseness

The body is lean and table-driven throughout — tool inventories with parameters ('`PDBeSIFTS_get_best_structures` (uniprot_id)'), a gotchas table ('`alphafold_get_prediction/summary` | `uniprot_id` | `qualifier`'), and threshold tables ('Resolution <2.0A (X-ray) / <3.0A (cryo-EM)') — with no explanations of concepts Claude already knows. Every section adds domain-specific knowledge Claude cannot infer, matching the level-5 anchor.

Actionability

Guidance is highly concrete: exact tool names with parameter signatures, correct-vs-mistake parameter pairs, artifact filter lists ('GOL, EDO, SO4, PEG'), and numeric decision thresholds. However, there are no fully executable example invocations with real values (e.g., a sample `PDBeSIFTS_get_best_structures` call with a real UniProt ID like 'P04637' in context), so it sits at 'mostly executable with minor gaps' rather than copy-paste-ready level 5.

Workflow Clarity

Three workflows are clearly phased (Workflow 1 Phases 0–5, Workflow 3 Phases 1–8) with decision rules ('Resolution <2.5A for drug design. X-ray > Cryo-EM > NMR > AlphaFold') and validation checkpoints such as Workflow 3's 'PDBeValidation quality → binding site well-resolved?'. It falls short of level 5 because there are no explicit error-recovery/feedback loops (what to do when a phase returns nothing, e.g., no co-crystal exists) even though the skill is read-only analysis rather than a destructive or batch operation, so the level-3 cap does not apply.

Progressive Disclosure

The single file is well-organized into scannable sections (LOOK UP DON'T GUESS, Tool Inventory, Workflows, Gotchas, Evidence Grading, Interpretation, Limitations) with no nested references, and no bundle files exist so everything is appropriately self-contained. It is above level 3 (structure is good and nothing is buried), but at ~125 lines the tool inventory and interpretation tables are bulk reference material that could arguably live in a separate reference file, keeping it at 'good structure with minor organization gaps' rather than level 5.

Specificity

The description enumerates concrete actions — 'druggability assessment, binding-site characterization, ligand-pocket analysis, structural-confidence scoring (resolution, pLDDT), and antibody-target interface analysis' — alongside the specific data sources combined (PDB, AlphaFold, GPCRdb, SAbDab, ProteinsPlus, BindingDB). Multiple specific concrete actions with comprehensive coverage matches the level-5 anchor; there is no generic filler to push it down.

Completeness

It explicitly answers 'what' ('Combines PDB experimental structures, AlphaFold predictions, GPCRdb, SAbDab antibody structures, ProteinsPlus binding-site prediction, and BindingDB ligand-affinity data') and 'when' via an explicit 'Use for' clause listing five concrete use cases. Both are explicit and concrete, matching the level-5 anchor; it is not the level-4 case because the 'when' clause is already specific and enumerated rather than needing more detail.

Trigger Term Quality

Natural domain phrases a user would say — 'drug target validation', 'druggability', 'binding site', 'antibody', 'AlphaFold' — are present, but coverage is not comprehensive: common variations like 'protein structure', 'cryo-EM', 'co-crystal', or file/database extensions a user might mention are missing. Good coverage with a few natural terms missing fits the level-4 anchor; it is above the partial-keyword level 3 but below the comprehensive synonym coverage of level 5.

Distinctiveness Conflict Risk

The niche is sharply defined by named databases and use cases (SAbDab antibody structures, GPCRdb, BindingDB ligand-affinity, structural-confidence scoring), giving it distinct triggers with minimal overlap risk against generic structural-biology or proteomics skills. This matches the level-5 anchor for a clear niche with distinct triggers.