devcontainer

devcontainer is a skill for Claude Code, Codex from event4u-app/agent-config. It costs 43 tokens per session (1,001 once invoked), scanned A, original, MIT.

A setup guide for Dev Containers and GitHub Codespaces, which provide reproducible development environments using configuration files and container images.

In plain words
What is it for?
It is for configuring development containers, Codespaces, VS Code features, secrets, environment variables, port forwarding, and container builds.
Why use it?
It helps teams avoid differences between local development environments and gives new contributors a consistent setup.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit It is for configuring development containers, Codespaces, VS Code features, secrets, environment variables, port forwarding, and container builds.

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Install with agentmods
npx agentmods add skills/event4u-app/agent-config/devcontainer
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 event4u-app/agent-config --skill devcontainer
Clone the repo
git clone --depth 1 https://github.com/event4u-app/agent-config

Made for: Claude Code, Codex.

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 devcontainer

README.md
[![agentmods](https://agentmods.dev/badge/skills/event4u-app/agent-config/devcontainer/github.svg)](https://agentmods.dev/skills/event4u-app/agent-config/devcontainer)
Your own site
<a href="https://agentmods.dev/skills/event4u-app/agent-config/devcontainer"><img src="https://agentmods.dev/badge/skills/event4u-app/agent-config/devcontainer/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 devcontainer

Your own site · 80×15
<a href="https://agentmods.dev/skills/event4u-app/agent-config/devcontainer"><img src="https://agentmods.dev/badge/skills/event4u-app/agent-config/devcontainer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 43 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,001 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 $0.00043 $0.01001
Opus 5 $0.00022 $0.00500
Sonnet 5 $0.00009 $0.00200
Haiku 4.5 $0.00004 $0.00100

Measured 7d ago against content hash 24b3aa751769, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

devcontainer 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 7d 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.

src/skills/devcontainer/SKILL.md · 127 lines

How it starts

The opening of the file, as written. The whole thing — 127 lines — stays where its author put it; the contents beside it link to each section on GitHub.

devcontainer

When to use

Use this skill when working with DevContainer configuration, GitHub Codespaces setup, or development environment standardization.

Do NOT use when:

  • Local Docker setup without Codespaces (use docker skill)
  • Production deployment (use aws-infrastructure skill)

Procedure: Modify DevContainer

  1. Gather context — read .devcontainer/devcontainer.json, check .devcontainer/ for env files and docs, check agents/overrides/skills/devcontainer.md for project-specific overrides.
  2. Identify change type — classify: image change, feature addition, secret addition, extension change, or env var change.
  3. Make the change — edit devcontainer.json (or related files). Follow conventions below for secrets, features, and environment variables.
  4. Build and verify — run devcontainer build to confirm the container builds. Check that extensions load and ports forward correctly.
  5. Document — if adding a new secret or dependency, update the onboarding docs in .devcontainer/.

Architecture

Custom image

DevContainers typically use a pre-built custom image hosted on a container registry (GHCR, ECR, Docker Hub). Read devcontainer.json for the image URL.

The image should include:

  • Language runtime (PHP, Node.js, Python, etc.)
  • Package managers (Composer, npm, etc.)
  • Common development tools

Features (installed on top of the image)

Common features:

Feature Purpose
git Git version control
github-cli GitHub CLI (gh) for API access
docker-in-docker Run Docker inside the DevContainer

Secrets management

Secrets can be managed via:

  • File mounts: .devcontainer/.secrets/<NAME>/run/secrets/<NAME>
  • GitHub Codespaces secrets: configured in the repository settings
  • Environment variables: in .devcontainer/devcontainer.env

Read devcontainer.json for the actual secret definitions and requirements.

Workspace

  • Workspace folder: typically /workspace or /workspaces/{repo-name}
  • Mount type: bind mount from local workspace
  • Container name and hostname: defined in devcontainer.json

Read the full file on GitHub · 127 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. 7d ago First seen · 127 lines · 43 tokens per session scan A 24b3aa751769

Subscribe to this mod's changes

devcontainer is a skill published in the GitHub repository event4u-app/agent-config (10 stars, last pushed today), licensed MIT. It adds 43 tokens to every session and 1,001 once invoked, about $0.0002 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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