Conciseness

The body is mostly efficient and concrete, but sections restate general Docker knowledge Claude already has — the multi-stage/layer-combining/cache-ordering examples in "Optimization Analysis", the "Non-Obvious Checks" table entries that are standard practice, a marketing-style "Key Features" checklist, and a generic "Notes" list that repeats earlier guidance. This matches the 3 anchor (mostly efficient but includes some unnecessary explanation or could be tightened); it is above 2 because there is no concept tutorial padding and most sections carry specific commands, but below 4 because sections 3–5 (~90 lines) duplicate content already split into references/optimization_guide.md and references/docker_best_practices.md.

Actionability

Guidance is copy-paste ready throughout: exact script invocation (`bash scripts/dockerfile-validate.sh Dockerfile`), executable hadolint/checkov/grep commands with flags, complete Dockerfile snippets for each optimization, a test-force flag (`FORCE_TEMP_INSTALL=true`), and a troubleshooting table mapping specific errors to specific fixes. This matches the 5 anchor — fully executable commands covering the common cases with no gaps.

Workflow Clarity

The "Mandatory Workflow" gives a clear ordered sequence (read → validate → summarize by severity → conditionally load reference files → propose fixes → ask → apply) with an 8-step example interaction, and "Handling Missing Tools" provides an explicit error-recovery feedback loop (auto-install fails → complete available validations → give install guidance → offer rerun). This matches the 5 anchor (clear sequence, explicit checkpoints, feedback loops for error recovery); the operation is validation itself rather than a destructive change, so the batch/destruction cap does not apply.

Progressive Disclosure

The bundle is real and well-signaled — every references/, scripts/, and assets/ file exists, is referenced inline at point of need, and is catalogued with purpose in the References section, all one level deep. It falls short of the 5 anchor on two organization gaps: sections 3–5 inline substantial content that duplicates the bundled reference files, and two reference descriptions overstate their contents ("full hadolint DL/SC rule listings" and "full CKV_DOCKER_* check listings" — neither rule listing actually appears in those files), which misdirects navigation. It is well above the 3 anchor because the split is otherwise appropriate and clearly signaled.

Specificity

The description enumerates six concrete, distinct actions — "running syntax checking, detecting security vulnerabilities, validating layer ordering, checking for hardcoded secrets, verifying base image tags, and analyzing build optimization" — which matches the anchor for multiple specific concrete actions with comprehensive coverage. It is not a 4 because there are no minor gaps in the action coverage; it is not below 5 because every capability is named as an executable check rather than generic language.

Completeness

It explicitly answers both questions: the first sentence states what the skill does (six named validation activities) and the second gives an explicit "Use when ..." clause with five concrete trigger phrases. This is a direct match for the 5 anchor (clear what AND when with concrete triggers); a 4 would require the when-clause to be less explicit or specific.

Trigger Term Quality

The "Use when" clause covers the natural phrases users would say — "validating Dockerfile syntax", "checking security best practices", "optimizing image builds", "auditing container security", "debugging Dockerfile errors" — and the closing sentence adds file-extension variants ("Dockerfile, Dockerfile.prod, Dockerfile.dev"), matching the anchor for comprehensive natural terms including synonyms and extensions. It exceeds the 4 anchor because no common variation (lint, secure, optimize, audit, debug) is missing.

Distinctiveness Conflict Risk

The niche is unambiguous — Dockerfile validation/security/optimization — with triggers (validate, lint, secure, audit) clearly distinct from adjacent skills like Dockerfile generation, and the scope note "Applies to all Dockerfile variants" further delimits it. Conflict risk is minimal, matching the 5 anchor for a clear niche with distinct triggers.