dockerfile

dockerfile is a skill for Claude Code from napalmpapalam/skills. It costs 106 tokens per session (1,597 once invoked), scanned D, original, MIT.

A detailed rule set for writing, editing, or reviewing Dockerfiles and related container builds. It covers base images, build context, caching, multi-stage builds, secrets, users, and process handling.

In plain words
What is it for?
Use it when creating or reviewing a Dockerfile, `.dockerignore`, or container image build.
Why use it?
It helps avoid large or unreproducible images, leaking secrets into image layers, and containers that handle processes incorrectly. It also defines safer defaults such as pinned image versions and a `.dockerignore` file.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Needs its repository: it runs a file that does not travel with it, so clone the repository first. The line is RUN CGO_ENABLED=0 go build -o /out/app ./cmd/app.

Part of the dd:docker plugin — 1 skill shipped together

Good fit Use it when creating or reviewing a Dockerfile, .dockerignore, or container image build.

Compare 6 skills from other repositories ↓
Install

Getting it into your agent

It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.

Clone the repo
git clone --depth 1 https://github.com/napalmpapalam/skills
agentmods
npx agentmods add skills/napalmpapalam/skills/dockerfile

Made for: Claude Code.

Or install dd:docker, the plugin that ships this one along with the rest of its 1 skill.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for dockerfile

README.md
[![agentmods](https://agentmods.dev/badge/skills/napalmpapalam/skills/dockerfile/github.svg)](https://agentmods.dev/skills/napalmpapalam/skills/dockerfile)
Your own site
<a href="https://agentmods.dev/skills/napalmpapalam/skills/dockerfile"><img src="https://agentmods.dev/badge/skills/napalmpapalam/skills/dockerfile/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for dockerfile

Your own site · 80×15
<a href="https://agentmods.dev/skills/napalmpapalam/skills/dockerfile"><img src="https://agentmods.dev/badge/skills/napalmpapalam/skills/dockerfile.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 106 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,597 The whole file, excluding the scripts and references it only reads on demand.
Security scan D 3 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00106 $0.01597
Opus 5 $0.00053 $0.00798
Sonnet 5 $0.00021 $0.00319
Haiku 4.5 $0.00011 $0.00160

Measured 4d ago against content hash 9e11fd930a3f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-17, from the pricing page.

Security

Grade D, and why

dockerfile scanned grade D with 3 findings 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 4d ago.

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.

Asks for rootmediumPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

Containers run as root by default. A container escape then starts from root on the host.

Recursive force deletehighDestructive command

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

&& rm -rf /var/lib/apt/lists/*

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

&& apt-get install -y --no-install-recommends curl ca-certificates \
plugins/docker/skills/dockerfile/SKILL.md · 168 lines

How it starts

The opening of the file, as written. The whole thing — 168 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Dockerfile Rules

Four goals, in this order: correct runtime, small image, fast cache, no secrets in layers. A layer is immutable — anything a layer writes ships in the image, even if a later layer deletes it.

Base image

  • Pick the smallest base that runs the artifact:
    • Distroless — compiled binaries with no shell needed. Smallest attack surface.
    • Alpine — static binaries, Go, Rust. musl, so check C dependencies first.
    • Slim — Python, Node.js. Debian userland without the build toolchain.
  • Pin an exact tag. Never latest — the build stops being reproducible the moment upstream moves.
  • Pin the digest when the build must be byte-identical: node:22.11.0-alpine@sha256:….
FROM node:22.11.0-alpine      # good — deterministic
FROM node:latest              # bad — a different image every rebuild

Build context

The daemon receives the whole context directory before the build starts. A large context slows every build, even a fully cached one.

  • Keep the context to the directory the build actually reads.
  • Always write a .dockerignore. It cuts upload time and keeps secrets out of the image.
.git
node_modules
target
dist
*.log
.env
.env.*
**/*.pem

Layer cache

Docker invalidates a layer and every layer after it when its inputs change. So order the file by change frequency: rarely-changed inputs first, source code last.

  • Copy the manifests, install dependencies, then copy the source. Source edits then reuse the dependency layer.
COPY package.json package-lock.json ./
RUN npm ci                    # cached until the manifests change
COPY . .                      # invalidated by every source edit
  • Chain one RUN per logical step with && and \. Clean the package cache inside the same RUN — a separate RUN rm leaves the files in the earlier layer.
RUN apt-get update \
 && apt-get install -y --no-install-recommends curl ca-certificates \
 && rm -rf /var/lib/apt/lists/*

Read the full file on GitHub · 168 lines

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. 4d ago First seen · 168 lines · 106 tokens per session scan D 9e11fd930a3f

Subscribe to this mod's changes

dockerfile is a skill published in the GitHub repository napalmpapalam/skills (4 stars, last pushed 5d ago), licensed MIT. It adds 106 tokens to every session and 1,597 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it D with 3 findings (asks for root, recursive force delete, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-13.

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