Docker

What it does

When your agent uses it

• Auditing a Dockerfile
• Shrinking a bloated image
• Hardening a container that runs as root
• Picking a base image

Example prompts

• “/docker”

Requirements

• Python 3
• A Bash shell
• Docker
• A credential in NPM_TOKEN

What it can do on your machine

Read from SKILL.md and the folder at commit 92fde8f. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 1 file in scripts/ (Shell), which the agent can run.

  Shell commands in SKILL.md call:

  • docker
  • trivy
  • apt-get
  • npm
  • hadolint
  • sh

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

• Network

  No URLs in SKILL.md. Its commands use docker and npm, 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:

  • NPM_TOKEN
  • POSTGRES_PASSWORD

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

Context cost

Docker loads about 2.7k tokens when it runs, and up to ~4.6k if it reads all its reference files. Until then it costs about 89 tokens; SKILL.md has 913 words of instructions outside code blocks.

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

~89

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

~2.7k

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

~4.6k

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

• NoteMentions a .env fileSKILL.md:127

  text (including `.git`, `node_modules`, `.env`) ships to the daemon: it

• NoteMentions a .env fileSKILL.md:135

  .env

• NoteMentions a .env fileSKILL.md:136

  .env.*

• NoteMentions a .env fileSKILL.md:248

  + build outputs | whole context ships; `.env`/`.git` can leak |

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); the scripts in this folder are not scanned.

SKILL.md

The full file from ericrisco/rsc-harness at commit 92fde8f, republished under its MIT licence (© ericrisco). 913 words, ~2,729 tokens.

name

docker

description

Use when authoring or auditing a Dockerfile, shrinking a bloated image, hardening a container that runs as root, picking a base image, or wiring a Compose dev loop with hot reload. NOT CI builds or deploy-to-host (that is `deployment`), NOT k8s autoscaling (that is `scaling`), NOT app-level injection or secrets-in-code (that is `secure-coding`).

tags

docker, containers, dockerfile, compose, image-security

recommends

deployment, secure-coding, scaling, github-actions

origin

risco

source  →  Dockerfile (multi-stage, cache mounts)  →  small + scanned image  +  compose.yaml (dev loop)
                                                            └──────────────┬──────────────┘
                                                    hand off to ../deployment/SKILL.md

# syntax=docker/dockerfile:1
FROM node:24-bookworm-slim AS build
WORKDIR /app
COPY package.json package-lock.json ./
RUN --mount=type=cache,target=/root/.npm npm ci
COPY . .
RUN npm run build && npm prune --omit=dev

FROM gcr.io/distroless/nodejs24-debian13:nonroot
WORKDIR /app
COPY --from=build /app/node_modules ./node_modules
COPY --from=build /app/dist ./dist
USER nonroot
EXPOSE 3000
HEALTHCHECK --interval=30s --timeout=3s CMD ["node", "dist/healthcheck.js"]
CMD ["dist/server.js"]

# syntax=docker/dockerfile:1
FROM python:3.13-slim-bookworm AS build
COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv
WORKDIR /app
ENV UV_PROJECT_ENVIRONMENT=/opt/venv
COPY pyproject.toml uv.lock ./
RUN --mount=type=cache,target=/root/.cache/uv uv sync --frozen --no-dev

FROM python:3.13-slim-bookworm
RUN useradd --create-home --uid 10001 app
COPY --from=build --chown=app:app /opt/venv /opt/venv
COPY --chown=app:app . /app
WORKDIR /app
ENV PATH="/opt/venv/bin:$PATH"
USER app
EXPOSE 8000
HEALTHCHECK CMD ["python", "-c", "import urllib.request,sys; sys.exit(0 if urllib.request.urlopen('http://localhost:8000/health').status==200 else 1)"]
CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]

# syntax=docker/dockerfile:1
FROM golang:1.26-bookworm AS build
WORKDIR /src
COPY go.mod go.sum ./
RUN --mount=type=cache,target=/go/pkg/mod go mod download
COPY . .
RUN --mount=type=cache,target=/root/.cache/go-build \
    CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o /app ./cmd/server

FROM scratch
COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=build /app /app
USER 10001:10001
EXPOSE 8080
ENTRYPOINT ["/app"]

.git
.gitignore
node_modules
dist
.env
.env.*
*.log
.venv
__pycache__
Dockerfile
.dockerignore
README.md

docker run \
  --read-only --tmpfs /tmp \
  --security-opt=no-new-privileges \
  --cap-drop=ALL \
  myimage:1.4.0

# Bad — leaks into image history:  ARG NPM_TOKEN
# Good:
RUN --mount=type=secret,id=npm_token \
    NPM_TOKEN="$(cat /run/secrets/npm_token)" npm ci

docker build --secret id=npm_token,env=NPM_TOKEN .

services:
  api:
    build: .
    ports: ["8000:8000"]
    depends_on:
      db:
        condition: service_healthy
    develop:
      watch:
        - action: sync          # hot-reload: copy changed files into the container
          path: ./src
          target: /app/src
        - action: rebuild       # lockfile / compiled langs: rebuild the image
          path: ./uv.lock
        - action: sync+restart  # config change: sync then restart the process
          path: ./config.yaml
          target: /app/config.yaml
  db:
    image: postgres:17-bookworm
    environment:
      POSTGRES_PASSWORD: dev
    volumes: ["pgdata:/var/lib/postgresql/data"]
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 5s
      timeout: 3s
      retries: 5
  seed:
    profiles: ["tools"]         # only runs with: docker compose --profile tools up
    build: .
    command: ["python", "-m", "app.seed"]

volumes:
  pgdata:

© ericrisco, 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 5 other files (scripts, references) in skills/docker of ericrisco/rsc-harness.

• SKILL.md
• evals/README.md
• evals/cases.yaml
• references/base-images-and-stages.md
• references/compose-recipes.md
• scripts/verify.sh

Open the folder on GitHubat commit 92fde8f