docker

docker is a skill for Claude Code from kumaran-is/claude-code-onboarding. It costs 92 tokens per session (1,260 once invoked), scanned A, original, MIT.

A Docker helper for writing and reviewing Dockerfiles, Docker Compose files, and .dockerignore files for backend services. Docker packages an application and its dependencies into a container that can run consistently in different environments.

In plain words
What is it for?
Use it to containerize NestJS, Spring Boot, Python/FastAPI, or TypeScript/Fastify services. It also helps with Compose setup, build failures, image size, security hardening, and multi-architecture builds.
Why use it?
Container builds can be slow, oversized, insecure, or fail only after deployment. This helps check build structure, user permissions, health checks, caching, secrets, and multi-platform images.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit Use it to containerize NestJS, Spring Boot, Python/FastAPI, or TypeScript/Fastify services. It also helps with Compose setup, build failures, image size, security hardening, and multi-architecture builds.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/kumaran-is/claude-code-onboarding/docker
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.

Any agent
npx skills add kumaran-is/claude-code-onboarding --skill docker
Clone the repo
git clone --depth 1 https://github.com/kumaran-is/claude-code-onboarding

Made for: Claude Code.

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 docker

README.md
[![agentmods](https://agentmods.dev/badge/skills/kumaran-is/claude-code-onboarding/docker/github.svg)](https://agentmods.dev/skills/kumaran-is/claude-code-onboarding/docker)
Your own site
<a href="https://agentmods.dev/skills/kumaran-is/claude-code-onboarding/docker"><img src="https://agentmods.dev/badge/skills/kumaran-is/claude-code-onboarding/docker/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 docker

Your own site · 80×15
<a href="https://agentmods.dev/skills/kumaran-is/claude-code-onboarding/docker"><img src="https://agentmods.dev/badge/skills/kumaran-is/claude-code-onboarding/docker.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 92 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,260 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 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 $0.00092 $0.01260
Opus 5 $0.00046 $0.00630
Sonnet 5 $0.00018 $0.00252
Haiku 4.5 $0.00009 $0.00126

Measured 6d ago against content hash 61401e771018, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

docker scanned grade A with 0 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 6d 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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/docker/SKILL.md · 97 lines

How it starts

The opening of the file, as written. The whole thing — 97 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Iron Law

NO DOCKERFILE WITHOUT READING reference/dockerfiles.md FIRST — each stack has specific base images, build tools, and health check patterns that must be used exactly

Docker

Production-ready containerization for NestJS/Node 24, Spring Boot WebFlux 3.5.x/Java 21, Python FastAPI 3.14, and TypeScript/Fastify/Node 24. All patterns follow: multi-stage build, non-root user, HEALTHCHECK, .dockerignore.

When to Use

  • Writing a Dockerfile for any backend service
  • Writing or updating docker-compose files for local dev or production
  • Reviewing an existing Dockerfile for security, size, or correctness
  • Adding build cache optimization (--mount=type=cache)
  • Setting up Docker Compose secrets for production
  • Building multi-architecture images (linux/amd64 + linux/arm64)
  • Debugging container build failures, slow builds, or large image sizes

How This Skill Relates to Others

Skill Scope
docker (this skill) Container definitions, compose files, build patterns
java-spring-api Java application code — loads docker skill for Dockerfile
nestjs-api NestJS templates include Dockerfile — this skill extends those patterns
python-dev FastAPI code — loads docker skill for Dockerfile
agentic-ai-dev Python agent code — has deployment reference that this skill augments

Process

Step 1: Choose the Right Dockerfile Pattern

Read reference/dockerfiles.md for the complete, copy-ready Dockerfile for your stack:

Stack Base Image Build Tool Port
NestJS 11.x / Node 24 node:24-alpine pnpm 3000
Spring Boot WebFlux 3.5.x maven:3.9-eclipse-temurin-21-alpine → eclipse-temurin:21-jre-alpine Maven 8080
Python FastAPI 3.14 python:3.14-slim uv 8000
Python Agentic AI python:3.14-slim uv + gunicorn 8000
TypeScript/Fastify / Node 24 node:24-alpine npm 3000

Step 2: Set Up Docker Compose

Read reference/compose-patterns.md for:

  • Development compose (PostgreSQL 17 + Redis 7)
  • Production compose with Docker secrets (_FILE env pattern)
  • Health check dependency ordering (condition: service_healthy)
  • Network isolation (internal backend network)
  • Resource limits and restart policies

Read the full file on GitHub · 97 lines

Files

What ships with it

4 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. 6d ago First seen · 97 lines · 0 tokens per session scan A 61401e771018

Subscribe to this mod's changes

docker is a skill published in the GitHub repository kumaran-is/claude-code-onboarding (35 stars, last pushed 2mo ago), licensed MIT. It adds 92 tokens to every session and 1,260 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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