The body is information-dense and avoids explaining basics Claude knows, but at ~170 lines wrapping a single atomic tool it is on the verbose side: the "When to use" section partly reiterates the description and several step prose blocks could be tightened.

Concrete, copy-paste-ready Python with real values — Structure_annotate_per_residue(pdb_id="6VJJ", ...), the assert landmark check, and the by_pos lookup — fully executable rather than pseudocode.

Five clearly sequenced steps with an explicit validation checkpoint (Step 3 verify-numbering assert plus offset-recovery guidance and "Do not silently rebase positions"), providing a real feedback loop for a fragile join operation.

No bundle files are provided and none are needed; the single self-contained file is well organized with clear section headers and a one-level cross-reference table, so the simple-skill allowance applies.

Lists multiple concrete actions ("produce a per-residue annotation table", "which residues sit at a binding interface", "which line a ligand pocket", "buried (core) vs solvent-exposed"), which meets the 3 anchor, but the trigger clause uses second person ("Use when you need to anchor"), so the rubric's voice guideline reduces specificity by 1.

It explicitly answers both what ("produce a per-residue annotation table" with the listed classifications) and when ("Use when you need to anchor a variant-interpretation or DMS analysis"), matching the explicit-trigger anchor.

The "Use when" clause and body include natural domain terms a user would say — "variant-interpretation", "DMS analysis", "PDB structure", "binding interface", "ligand pocket" — giving good coverage rather than abstract jargon.

The niche is sharp — a per-residue structural annotation track drawn under a DMS heatmap — and the role-relative-to-partner-chain framing makes it unlikely to trigger for the wrong skill.