Skills Guide

Dockerfile Review

VerifiedSafe

Audit Dockerfiles for security, efficiency, and best practices. Identify critical issues, warnings, and suggestions with corrected code examples.

Download and use
Sby Skills Guide Bot
DevOpsIntermediate
3/8/2026
Claude CodeCursorWindsurfCopilotCodex
#docker#container-security#image-optimization#code-review#best-practices

Recommended for

Backend developerClaude CodeCode reviewCursorCopilotDevOps engineer

Automated summary

Audits a Dockerfile for security, efficiency, and best practices, then reports issues by severity with concrete fixes.

Strengths

  • Groups findings by severity (critical, warning, suggestion) with line references
  • Covers concrete security checks: hardcoded secrets, root execution, missing USER, curl | sh patterns
  • Suggests fixes as corrected Dockerfile code, including BuildKit cache mounts
  • Also verifies that a .dockerignore exists and covers items like .git and node_modules

Limitations

  • Purely static review: it does not build or run the image, so installed-package CVEs go unchecked
  • Relies on Read, Glob, and Grep only, with no scanner integration such as Trivy or Hadolint
  • Does not quantify the actual image-size savings from its optimization advice
When to use it

Use it to audit an existing Dockerfile before merging changes or publishing a container image.

When not to use it

Don't use it to scan an already-built image for CVEs or to write a Dockerfile from scratch.

Security analysis

Safe
Quality score90/100

The skill uses only read-only tools (Read, Glob, Grep) and provides defensive review guidance for Dockerfiles. It does not execute commands, access networks, exfiltrate data, or instruct destructive actions.

No concerns found

How this analysis is made

Examples

Review a Node Dockerfile
Review my Dockerfile — it's using node:latest and I'm worried it's bloated and insecure.
Shrink the image
Can you look at ./Dockerfile and suggest how to reduce image size and fix layer ordering?
Security audit
Audit this Dockerfile for security issues and check whether my .dockerignore covers .git and node_modules.

name: dockerfile-review description: Review Dockerfiles for best practices, security, and optimization. Use when the user says "review Dockerfile", "optimize image", "Dockerfile best practices", "reduce image size", or asks to audit a container build. allowed-tools: Read, Glob, Grep

Dockerfile Review

Audit Dockerfiles for security, efficiency, and best practices.

Instructions

  1. Read the Dockerfile
  2. Check for issues in each category below
  3. Report findings with severity (critical/warning/suggestion)
  4. Provide specific fixes with corrected code

Security checks

  • MUST flag USER root without switching back
  • MUST flag secrets in ENV, ARG, or COPY (API keys, passwords)
  • MUST flag apt-get install without --no-install-recommends
  • Flag missing USER directive (runs as root by default)
  • Flag COPY . . (may include secrets, .git, etc.)
  • Flag :latest tags (unpinned versions)
  • Flag curl | sh patterns

Optimization checks

  • Multi-stage builds for compiled languages
  • Layer ordering (least-changing first)
  • Combined RUN statements to reduce layers
  • Cache mounts for package managers: --mount=type=cache
  • .dockerignore file exists and covers .git, node_modules, etc.
  • apt-get clean && rm -rf /var/lib/apt/lists/* in same layer

Best practices

# Good: pinned, non-root, minimal
FROM python:3.11-slim@sha256:abc123...
WORKDIR /app
RUN useradd -r -s /bin/false appuser
COPY requirements.txt .
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install -r requirements.txt
COPY --chown=appuser:appuser . .
USER appuser
CMD ["python", "app.py"]

Output format

## Critical
- Line 5: Running as root without USER directive

## Warnings
- Line 12: Using :latest tag - pin to specific version

## Suggestions
- Line 8-10: Combine RUN statements to reduce layers

Rules

  • MUST read the Dockerfile before reviewing
  • MUST categorize issues by severity
  • Never approve Dockerfiles with hardcoded secrets
  • Always check for corresponding .dockerignore

From the file to a first result

The download contains exactly the content displayed on this page. This copy may differ from the latest version in the source repository.

View the source and supporting files

This download contains SKILL.md only. Any scripts, references, templates and dependencies are not included. Get the required files from the source, preserving their directory structure, before continuing.

1. Download the file

Download SKILL.md

From the root of a test project, save the file as .skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md, or use the command below. This folder is for inspecting the skill before installation.

Command for macOS/Linux or WSL: requires a POSIX shell and curl. On Windows without WSL, use the download button and create the folder manually.

mkdir -p '.skill-downloads/dockerfile-review-mmh8qqpm' && curl --fail --show-error --location 'https://skills-guides.com/api/skills/dockerfile-review-mmh8qqpm/download' --output '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md.part' && mv '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md.part' '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md'

2. Check prerequisites

Read SKILL.md before using it. If it references scripts or external services, inspect them and prepare the required access in your test environment.

Tools declared by the author (check availability in your agent): Read, Glob, Grep

No recognized prerequisites section in this file. This does not mean it is self-contained: libraries, tools and access requirements may be mentioned elsewhere in the content or source repository.

The platforms on this page are catalog indications. The paths below follow tool documentation; they do not prove this skill has been run in those tools. No minimum tool version is confirmed for this listing.

3. Load the skill

After inspection, copy the complete folder into your project using one of the commands below, then open a new tool session. The command stops if a folder with the same name already exists: compare the files before replacing it.

Claude Code
test -f '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && test -s '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && mkdir -p '.claude/skills' && test ! -e '.claude/skills/dockerfile-review' && cp -R '.skill-downloads/dockerfile-review-mmh8qqpm' '.claude/skills/dockerfile-review'

Cursor
test -f '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && test -s '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && mkdir -p '.cursor/skills' && test ! -e '.cursor/skills/dockerfile-review' && cp -R '.skill-downloads/dockerfile-review-mmh8qqpm' '.cursor/skills/dockerfile-review'

Codex
test -f '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && test -s '.skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md' && mkdir -p '.agents/skills' && test ! -e '.agents/skills/dockerfile-review' && cp -R '.skill-downloads/dockerfile-review-mmh8qqpm' '.agents/skills/dockerfile-review'

OpenSkills

OpenSkills must already be installed. The local install/read procedure is checked with OpenSkills 1.5.0, which requires Node.js ≥ 20.6.0. Catalog slugs are not resolved automatically.

Official OpenSkills installation
openskills install './.skill-downloads/dockerfile-review-mmh8qqpm'

openskills read 'dockerfile-review-mmh8qqpm'

Reading should display the installed file content and its base directory. It does not run the skill or install its dependencies.

For an agent that reads AGENTS.md, then sync the index. This command changes AGENTS.md: review the diff before using it.

openskills sync

Manual method or another tool: attach SKILL.md to a conversation, or open it in an agent that can read files. Include any required supporting resources. No universal folder is recognized by every tool.

4. Try a first task

Use a short, synthetic input: an API endpoint, a small document or an interface brief. In a new conversation, attach the file or give the agent its path, then adapt this request:

Read .skill-downloads/dockerfile-review-mmh8qqpm/SKILL.md and apply its instructions to this example: [describe a test input]. Identify any missing files, dependencies or access. Produce the result requested by the skill without inventing data or running unreviewed scripts.

Expected result: output matching the skill instructions, or a precise list of missing prerequisites. A read confirmation alone does not validate a first use. If an external resource is unavailable, that path remains untested.

Related skills

Configure a Chat Channel with SecretRefs

DevOps

Set up chat channels using non-interactive commands, with secrets only as SecretRefs. Covers gather, mutate, repair, and prove steps for reliable delivery.

Claude CodeCodexintermediateSafe 387,940
Skills Guide Bot

Investigate ClickHouse CI Failures

DevOps

Investigate a ClickHouse CI failure end-to-end from a PR or S3 report URL. Fetches failed tests, classifies flaky vs real regression, and checks for existing issues/fixes.

Claude CodeadvancedSafe 49,516
Skills Guide Bot

Ansible PR Review

DevOps

Reviews an Ansible PR following the project's standardized process, including changelog checks, test coverage validation, and feedback tracking.

Claude CodeintermediateSafe 70,491
Skills Guide Bot