Claude Code Devcontainer Sandbox

A template for running Claude Code inside a sandboxed devcontainer, intended for use with --dangerously-skip-permissions. The container runs as an unprivileged user with an egress firewall that restricts outbound traffic to a known allowlist.

Based on the official Anthropic devcontainer example.

Requirements

• VS Code with the Dev Containers extension
• Docker
• Copier (e.g. uv tool install copier)
• A GitHub personal access token with repo access

Setup

From your project directory, run:

copier copy gh:awgymer/slopbox .

Copier will ask for:

• a parent directory (default: .devcontainer),
• a container name (default: claude),
• an optional set of extra tools to install (see Optional tools).

The files are installed into <devcontainer_root>/<name>/.

Add devcontainer.env to your .gitignore, then open it at your project root and fill in your values:

GH_TOKEN=           # GitHub personal access token
GIT_AUTHOR_NAME=    # Your name for git commits
GIT_AUTHOR_EMAIL=   # Your email for git commits
GIT_COMMITTER_NAME=
GIT_COMMITTER_EMAIL=

Open the project in VS Code and select Reopen in Container.

Optional tools

During copier copy you can multi-select extra tools to install in the container:

• uv — Python package manager (Astral)
• Java (Temurin 21) — JDK from Adoptium
• Rust (rustup) — Rust toolchain (rustc, cargo) via rustup
• nextflow-bundle — java, nextflow, nf-test, uv, nf-core (with prek and pre-commit)
• aws-bundle — node (via nvm), aws-cdk, awscli

Bundles install dependencies automatically; selecting multiple choices dedupes. The resolved atomic tool list is stored as installed_tools in .copier-answers.yml.

Version overrides

Defaults are pinned in the installer scripts. To override at build time, pass build args to Docker or edit build.args in devcontainer.json:

Tool	ARG	Default
Nextflow	NEXTFLOW_VERSION	25.10.4
nf-test	NFT_VERSION	0.9.5
nf-core	NFCORE_VERSION	3.5.1
node	NODE_VERSION	22

Firewall additions

Selecting a tool that needs runtime network access auto-adds the relevant domains to extra-allowed-domains:

• uv → pypi.python.org, pypi.org, pythonhosted.org, files.pythonhosted.org
• node → nodejs.org
• rust → static.rust-lang.org, crates.io, index.crates.io, static.crates.io
• nextflow → nf-co.re, docs.seqera.io
• awscli → sts.amazonaws.com (add service-specific endpoints as needed)

Updating

To pull in template changes while keeping your local modifications:

copier update

Copier performs a 3-way merge, so changes to files like the Dockerfile are reconciled with your own additions. devcontainer.env is never overwritten.

Commit .copier-answers.yml to your repo so teammates can also run copier update.

Firewall

The container restricts outbound traffic to a fixed allowlist on startup. To permit additional domains, add them to extra-allowed-domains at your project root, one per line:

# extra-allowed-domains
pypi.org
api.mycompany.com

Lines starting with # and blank lines are ignored.

Customisation

• Add tools: pick from the prebuilt set via the extra_tools copier question (see Optional tools), or add custom installs in Dockerfile
• Shell config: edit zshrc in your chosen install directory before starting the container
• Prompt: replace p10k.zsh with your own Powerlevel10k config