Conciseness

The body is lean and assumes competence — no basic Docker/bake concept explanations, and justifications are compressed to single lines ('One line ends the question'). Score 4 rather than 5 because time-sensitive material (dates 2026-08-07/08-10, buildx v0.36.0, VERSION pins in prose) sits in a 'Last verified' section rather than an old-patterns/deprecated section, and a couple of anecdotal asides ('four authors in the wild disagreed') could be trimmed.

Actionability

Guidance is fully executable: a complete annotated Dockerfile, copy-paste commands (docker buildx bake --list=targets, sbx run -t docker.io/you/my-template:v1, gh auth token | sbx secret set --registry ghcr.io --password-stdin, docker image save ... -o t.tar), and both linked bundle files (assets/Dockerfile, assets/docker-bake.hcl) exist. Common cases are covered by specific examples.

Workflow Clarity

Sections follow the real sequence (pick base → write Dockerfile → bake family → publish/run → save sandbox) and include a pre-build checkpoint ('--list=targets # the expansion, before building anything') plus failure-mode warnings (missing contexts entry silently resolving to the registry). Score 4 rather than 5 because there is no explicit post-build verification step (e.g., smoke-testing a sandbox before --push).

Progressive Disclosure

Well-organized overview with essentials inline and fuller material split into real, one-level-deep, clearly signaled asset references ('A fuller version is in [assets/Dockerfile]', 'the matrix form is in [assets/docker-bake.hcl]'), both verified to exist. Headers make navigation easy and nothing that belongs in a separate file is inlined.

Specificity

The description names the concrete primary action ('Build a Docker Sandbox template image by extending docker/sandbox-templates') and enumerates multiple specific sub-actions — 'writing a Dockerfile for sbx, choosing a base variant, building a family of templates with bake, or publishing and loading one with sbx template' — giving comprehensive coverage of the skill's domain. Score 5 rather than 4 because no concrete capability area is noticeably missing.

Completeness

It explicitly answers 'what' ('Build a Docker Sandbox template image by extending docker/sandbox-templates') and 'when' with a concrete 'Use when...' clause listing four trigger scenarios. This matches the anchor-5 example structure (clear what + explicit when with concrete trigger phrases).

Trigger Term Quality

Good natural keyword coverage: 'Dockerfile', 'sandbox', 'template', 'bake', 'sbx', 'publish', 'load' — terms a user with this need would plausibly say. Score 4 rather than 5 because a few natural synonyms users might use ('custom sandbox image', 'container image') are absent.

Distinctiveness Conflict Risk

The niche is unambiguous — building sbx template images — and the triggers (Dockerfile for sbx, bake family, sbx template publish/load) are distinct from generic Docker work or run-time kit configuration, so conflict risk is minimal. Voice is imperative/third-person as in the good examples, with no vague fluff.