Docker Development

What it does

When your agent uses it

• Working with ANY Docker task: writing Dockerfiles
• Configuring docker-compose/compose.yml
• Multi-stage builds
• Docker-bake.hcl

Example prompts

• “/docker-development”

Requirements

• Node.js
• Docker
• Compatibility (from SKILL.md): Requires docker, docker compose.
• Pre-approved tools (allowed-tools): Bash(docker:*), Bash(grep:*), Read, Write, Glob, Grep

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

1. 1Minimal -- Alpine/distroless, multi-stage
2. 2Secure -- Non-root USER, no layer secrets, pin versions
3. 3Testable -- CI-verifiable: entrypoint bypass, DNS mocking
4. 4Cache-efficient -- deps first, clean in same layer

What it can do on your machine

Read from SKILL.md and the folder at commit c081a2d. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Bash(docker:*)
  • Bash(grep:*)
  • Read
  • Write
  • Glob
  • Grep

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • docker

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md. Its commands use docker, which can reach the network depending on how they are called.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names these keys or tokens, usually read from environment variables:

  • DB_PASSWORD

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

• Compatibility

  Requires docker, docker compose.

  From compatibility in the SKILL.md frontmatter.

Context cost

Docker Development loads about 1.1k tokens when it runs, and up to ~7.1k if it reads all its reference files. Until then it costs about 85 tokens; SKILL.md has 233 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~85

When it runs · the whole SKILL.md, loaded when a task matches

~1.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~7.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• WarningMentions a credentials file (SSH keys, cloud or package-manager tokens)SKILL.md:86

  t=type=secret,id=ssh_key,dst=/root/.ssh/id_rsa git clone git@github.com:org/repo.git

• NoteMentions a .env fileSKILL.md:117

  **Compose validation**: `cp .env.example .env` before `docker compose config`

• NoteMentions a .env fileSKILL.md:123

  clude: `.git`, `node_modules`/`vendor`, `.env*`, `*.pem`, `*.key`

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from JMBeresford/retrom at commit c081a2d, republished under its MIT licence (© JMBeresford). 233 words, ~1,085 tokens.

name

docker-development

description

Use when working with ANY Docker task: writing Dockerfiles, configuring docker-compose/compose.yml, multi-stage builds, docker-bake.hcl, container security audits, .dockerignore optimization, or CI/CD container testing. Triggers on: Dockerfile, docker-compose, container, image build, multi-stage, docker bake, compose.

allowed-tools

Bash(docker:*), Bash(grep:*), Read, Write, Glob, Grep

compatibility

Requires docker, docker compose.

license

(MIT AND CC-BY-SA-4.0)

metadata.version

1.10.0

metadata.repository

https://github.com/netresearch/docker-development-skill

metadata.author

Netresearch DTT GmbH

FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .

FROM node:20-alpine
RUN addgroup -g 1001 app && adduser -u 1001 -G app -D app
USER app
COPY --from=builder /app .
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD wget -qO- http://localhost:3000/health || exit 1
CMD ["node", "server.js"]

FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY go.* ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o /app/server .

FROM gcr.io/distroless/static:nonroot
COPY --from=builder /app/server /server
CMD ["/server"]

RUN apt-get update && \
    apt-get install -y --no-install-recommends curl && \
    rm -rf /var/lib/apt/lists/*

COPY package*.json ./
RUN npm ci
COPY . .

RUN --mount=type=secret,id=ssh_key,dst=/root/.ssh/id_rsa git clone git@github.com:org/repo.git

target "app" {
  platforms = ["linux/amd64", "linux/arm64"]
  cache-from = ["type=gha"]
  cache-to = ["type=gha,mode=max"]
}

© JMBeresford, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 3 other files (references) in .agents/skills/docker-development of JMBeresford/retrom.

• SKILL.md
• references/bind-mount-ownership.md
• references/ci-testing.md
• references/dind-testing-patterns.md

Open the folder on GitHubat commit c081a2d