devcontainer-setup

Devcontainer Setup Skill

Creates a pre-configured devcontainer with Claude Code and language-specific tooling.

When to Use

• User asks to "set up a devcontainer" or "add devcontainer support"
• User wants a sandboxed Claude Code development environment
• User needs isolated development environments with persistent configuration

When NOT to Use

• User already has a devcontainer configuration and just needs modifications
• User is asking about general Docker or container questions
• User wants to deploy production containers (this is for development only)

Workflow

flowchart TB
    start([User requests devcontainer])
    recon[1. Project Reconnaissance]
    detect[2. Detect Languages]
    generate[3. Generate Configuration]
    write[4. Write files to .devcontainer/]
    done([Done])
 
    start --> recon
    recon --> detect

Phase 1: Project Reconnaissance

Infer Project Name

Check in order (use first match):

1. package.json → name field
2. pyproject.toml → project.name
3. Cargo.toml → package.name
4. go.mod → module path (last segment after /)
5. Directory name as fallback

Convert to slug: lowercase, replace spaces/underscores with hyphens.

Detect Language Stack

Multi-Language Projects

If multiple languages are detected, configure all of them in the following priority order:

1. Python - Primary language, uses Dockerfile for uv + Python installation
2. Node/TypeScript - Uses devcontainer feature
3. Rust - Uses devcontainer feature
4. Go - Uses devcontainer feature

For multi-language postCreateCommand, chain all setup commands:

Extensions and settings from all detected languages should be merged into the configuration.

Phase 2: Generate Configuration

Start with base templates from resources/ directory. Substitute:

• {{PROJECT_NAME}} → Human-readable name (e.g., "My Project")
• {{PROJECT_SLUG}} → Slug for volumes (e.g., "my-project")

Then apply language-specific modifications below.

Base Template Features

The base template includes:

• Claude Code with marketplace plugins (anthropics/skills, trailofbits/skills, trailofbits/skills-curated)
• Sandboxing via bubblewrap and socat
• Python 3.13 via uv (fast binary download)
• Node 22 via fnm (Fast Node Manager)
• ast-grep for AST-based code search
• Network isolation tools (iptables, ipset) with NET_ADMIN capability
• Security mounts: .devcontainer/ mounted read-only to prevent container escape
• Token forwarding: CLAUDE_CODE_OAUTH_TOKEN and ANTHROPIC_API_KEY via remoteEnv
• Modern CLI tools: ripgrep, fd, fzf, tmux, git-delta

Language-Specific Sections

Python Projects

Detection: pyproject.toml, requirements.txt, setup.py, or *.py files

Dockerfile additions:

The base Dockerfile already includes Python 3.13 via uv. If a different version is required (detected from pyproject.toml), modify the Python installation:

devcontainer.json extensions:

Add to customizations.vscode.extensions:

Add to customizations.vscode.settings:

postCreateCommand: If pyproject.toml exists, chain commands:

Node/TypeScript Projects

Detection: package.json or tsconfig.json

No Dockerfile additions needed: The base template includes Node 22 via fnm (Fast Node Manager).

devcontainer.json extensions:

Add to customizations.vscode.extensions:

Add to customizations.vscode.settings:

postCreateCommand: Detect package manager from lockfile and chain with base command:

• pnpm-lock.yaml → uv run /opt/post_install.py && pnpm install --frozen-lockfile
• yarn.lock → uv run /opt/post_install.py && yarn install --frozen-lockfile
• package-lock.json → uv run /opt/post_install.py && npm ci
• No lockfile → uv run /opt/post_install.py && npm install

Rust Projects

Detection: Cargo.toml

Features to add:

devcontainer.json extensions:

Add to customizations.vscode.extensions:

Add to customizations.vscode.settings:

postCreateCommand: If Cargo.lock exists, use locked builds:

If no lockfile, use standard build:

Go Projects

Detection: go.mod

Features to add:

devcontainer.json extensions:

Add to customizations.vscode.extensions:

Add to customizations.vscode.settings:

postCreateCommand:

Reference Material

For additional guidance, see:

• references/dockerfile-best-practices.md - Layer optimization, multi-stage builds, architecture support
• references/features-vs-dockerfile.md - When to use devcontainer features vs custom Dockerfile

Adding Persistent Volumes

Pattern for new mounts in devcontainer.json:

Common additions:

• source={{PROJECT_SLUG}}-cargo-${devcontainerId},target=/home/vscode/.cargo,type=volume (Rust)
• source={{PROJECT_SLUG}}-go-${devcontainerId},target=/home/vscode/go,type=volume (Go)

Output Files

Generate these files in the project's .devcontainer/ directory:

1. Dockerfile - Container build instructions
2. devcontainer.json - VS Code/devcontainer configuration
3. post_install.py - Post-creation setup script
4. .zshrc - Shell configuration
5. install.sh - CLI helper for managing the devcontainer (devc command)

Validation Checklist

Before presenting files to the user, verify:

1. All {{PROJECT_NAME}} placeholders are replaced with the human-readable name
2. All {{PROJECT_SLUG}} placeholders are replaced with the slugified name
3. JSON syntax is valid in devcontainer.json (no trailing commas, proper nesting)
4. Language-specific extensions are added for all detected languages
5. postCreateCommand includes all required setup commands (chained with &&)

User Instructions

After generating, inform the user:

1. How to start: "Open in VS Code and select 'Reopen in Container'"
2. Alternative: devcontainer up --workspace-folder .
3. CLI helper: Run .devcontainer/install.sh self-install to add the devc command to PATH