dockerfile-pro

A skill for writing and reviewing Dockerfiles, the instructions used to build container images. It focuses on small, secure, repeatable builds for languages such as Go, Rust, Node, Python, Java, and .NET.

In plain words
What is it for?
It helps containerize applications, design multi-stage builds, choose runtime images, run as a non-root user, pin base images, improve build caching, use minimal final images, add health checks, and review image risks.
Why use it?
It helps avoid bloated images, unnecessary security exposure, leaked secrets, unpredictable dependencies, and slow rebuilds.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/jayrha/agentskills/dockerfile-pro
Any agent
npx skills add JayRHa/AgentSkills --skill dockerfile-pro
Clone the repo
git clone --depth 1 https://github.com/JayRHa/AgentSkills

Made for: Claude Code, Codex.

Per session 115 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,989 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00115 $0.01989
Opus 5 $0.00057 $0.00994
Sonnet 5 $0.00023 $0.00398
Haiku 4.5 $0.00012 $0.00199

Measured 2d ago against content hash aa6d97532f0b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

dockerfile-pro scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/check_dockerfile.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Recursive force deletemediumDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

- **Clean in the same layer:** `apt-get update && apt-get install -y --no-install-recommends X && rm -rf /var/lib/apt/lists/*`.

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

dockerfile-pro/SKILL.md · 91 lines

How it starts

The opening of the file, as written. The whole thing — 91 lines — stays where its author put it; the contents beside it link to each section on GitHub.

dockerfile-pro

Overview

Produce production-grade Dockerfiles that are small (minimal final image), secure (non-root, pinned, no secrets, minimal surface), and reproducible (deterministic builds with effective layer caching). Applies to any language runtime (Go, Rust, Node, Python, Java, .NET, etc.) and any registry.

Keywords: Dockerfile, container, multi-stage build, build cache, BuildKit, non-root user, distroless, alpine, slim, image size, layer caching, .dockerignore, HEALTHCHECK, OCI image, supply chain, reproducible build, hadolint, Trivy.

The three goals (small / secure / reproducible) often align, but when they conflict, prioritize security > reproducibility > size.

Workflow

Follow these steps in order when authoring or reviewing a Dockerfile.

  1. Identify the app shape. Compiled binary (Go/Rust/C++) → use a FROM scratch or distroless final stage. Interpreted/runtime (Node/Python/Java/.NET) → use the matching -slim/distroless runtime image. JVM/CLR may need a JRE-only final image.
  2. Always use multi-stage. A builder stage installs toolchains and compiles/installs dependencies; the final stage copies only the runtime artifacts. Never ship compilers, package caches, or dev headers.
  3. Pin everything. Pin the base image by tag and digest (image:tag@sha256:...). Pin OS and language package versions. This is what makes builds reproducible.
  4. Order layers from least- to most-frequently-changing. Copy dependency manifests (package.json, go.mod, requirements.txt, *.csproj) and install deps before copying application source. Source changes then don't bust the dependency layer.
  5. Use BuildKit cache mounts (RUN --mount=type=cache,...) for package-manager caches so repeated builds are fast without bloating the image.
  6. Drop to a non-root user in the final stage with an explicit numeric UID/GID. Make the filesystem read-only-friendly.
  7. Minimize layers and surface. Combine related RUN steps, clean package caches in the same layer, and copy with --chown instead of a separate chown layer.
  8. Add operational metadata. WORKDIR, EXPOSE, ENV, OCI LABELs, HEALTHCHECK, and an exec-form ENTRYPOINT/CMD.
  9. Add a .dockerignore. Exclude .git, node_modules, build output, secrets, and CI files so the build context stays small and secrets never enter an image.
  10. Lint and scan. Run hadolint Dockerfile and a vulnerability scan (e.g. trivy image). See scripts/check_dockerfile.py for a fast static audit you can run with zero dependencies.

Read the full file on GitHub · 91 lines

Files

What ships with it

8 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 91 lines · 115 tokens per session scan B aa6d97532f0b

Subscribe to this mod's changes

dockerfile-pro is a skill published in the GitHub repository JayRHa/AgentSkills (4 stars, last pushed 1mo ago), licensed MIT. It adds 115 tokens to every session and 1,989 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it B with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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