Conciseness

The body is largely efficient — concrete steps, tables, and code templates with little padding — but has minor trimmable explanation: the Overview re-explains what GTFOBins is ("documents Unix binaries that can be abused to bypass security restrictions") and the Notes section overlaps the Step 3 classification table. This matches anchor 4 (efficient with minor over-explanation) rather than 3, since the redundancy is localized, not pervasive.

Actionability

Guidance is mostly executable: exact source paths (`interp/builtins/builtins.go`), a test-file naming convention, three Go test patterns, and a copy-paste `go test ./interp/... -run TestCmdGTFOBins -timeout 120s -v` command. It falls short of anchor 5 because the code templates contain `<command>`, `<dangerous-flag>`, and `<gtfobins-technique>` placeholders requiring substitution — minor gaps rather than copy-paste-ready code.

Workflow Clarity

Six clearly sequenced steps include an explicit validation checkpoint and feedback loop — Step 5 says "Run the tests to confirm all GTFOBins techniques are blocked… Fix any test failures", with a re-run after fixes and a stop-and-report protocol for critical findings. This matches anchor 5 (explicit validation steps, error-recovery loops); anchor 4's 'minor validation gaps' does not apply.

Progressive Disclosure

The single-file body is well organized with clear sections (Workflow steps, test patterns, report format, Notes), and no bundle files exist to reference. The 'Known GTFOBins attack patterns for current builtins' section is per-command reference data that could be split into a separate file, keeping this at anchor 4 (good structure, minor organization gap) rather than 5.

Specificity

The description names a concrete domain and one clear action ("Validate shell builtins against GTFOBins attack patterns") plus a purpose ("to ensure exploits are blocked by the sandbox"), but does not list several distinct actions like test-writing or report generation. It fits anchor 3 (domain plus 1-2 concrete actions, not comprehensive) rather than 4, which requires several specific actions.

Completeness

The "what" is clear and concrete, but there is no "Use when…" clause or equivalent trigger guidance, capping completeness at 3 per the rubric guidelines. Not 4 because the "when" is entirely absent rather than just imprecise.

Trigger Term Quality

Natural trigger terms are present — "GTFOBins", "shell builtins", "exploits", "sandbox" — which a user needing this skill would plausibly say. A few natural variants are missing (e.g. "sandbox escape", "pentest", "security audit"), matching anchor 4 rather than 5's comprehensive synonym coverage.

Distinctiveness Conflict Risk

"GTFOBins" and "shell builtins" carve out a clear niche with distinct triggers; virtually no other skill would match this description, giving minimal conflict risk — matching anchor 5.