Container Layer

What it does

When your agent uses it

• The user mentions container layer
• Custom container
• Cache my installs
• Composable layers

Example prompts

• “container layer”
• “Containerfile”
• “custom container”
• “/container-layer”

Requirements

• Python 3
• A Bash shell
• Docker

Workflow steps

4 steps, taken from the first numbered list in SKILL.md.

1. 1Parses a Containerfile (Dockerfile subset) that declares your environment
2. 2Caches the built result as a tarball in GitHub Releases
3. 3Restores from cache on subsequent boots (single fetch vs. N installs)
4. 4Provides a uv shim that captures ad-hoc installs back into the Containerfile

What it can do on your machine

Read from SKILL.md and the folder at commit 6fc82b8. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 8 files in scripts/ (Python and Shell), which the agent can run.

  Shell commands in SKILL.md call:

  • python
  • uv

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md. Its commands use uv, which can reach the network depending on how they are called.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names these keys or tokens, usually read from environment variables:

  • GH_TOKEN

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Container Layer loads about 1.4k tokens when it runs. Until then it costs about 132 tokens; SKILL.md has 358 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~132

When it runs · the whole SKILL.md, loaded when a task matches

~1.4k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from oaustegard/claude-skills at commit 6fc82b8, republished under its MIT licence (© oaustegard). 358 words, ~1,446 tokens.

name

container-layer

description

Authors and caches a personalized container environment from a Dockerfile- like spec, as a single layer or as a composition of independently cached layers. Use when the user mentions "container layer", "Containerfile", "custom container", "cache my installs", "composable layers", "uv shim", or wants package installations, skills and environment config to survive an ephemeral session. Also for snapshotting, restoring or rebuilding that environment, and for capturing ad-hoc installs into a reproducible spec.

metadata.version

0.4.0

# Environment variables
ENV KEY=value

# Shell commands (including package installs)
RUN apt-get install -y foo        # system packages
RUN uv pip install pandas numpy   # Python packages (preferred)
RUN pip install requests          # also works

# Fetch files from URLs or GitHub
FETCH https://example.com/file.tar.gz /dest/path
FETCH github:user/repo /dest/path              # latest tarball
FETCH github:user/repo@ref /dest/path          # specific ref

# Set working directory for subsequent RUN commands
WORKDIR /some/path

# Declare paths to include in the cached layer snapshot
# (auto-detected for FETCH destinations and pip/uv installs)
SNAPSHOT /additional/path/to/capture

# Ignored (Dockerfile compat, no-op here):
# FROM, EXPOSE, CMD, ENTRYPOINT, LABEL, ARG, VOLUME, USER, SHELL

from scripts.containerfile import ContainerLayer

layer = ContainerLayer(
    containerfile_path="/path/to/Containerfile",
    cache_repo="oaustegard/claude-container-layers",  # GitHub repo for release assets
    gh_token="...",
)

# Try cache first, fall back to full build
layer.restore_or_build()

python -m scripts.cli restore /path/to/Containerfile --repo user/cache-repo

from scripts.containerfile import compose

compose(
    containerfile_paths=[
        "layers/Containerfile",            # name='base'  (always-on)
        "layers/Containerfile.scientific", # name='scientific'
        "layers/Containerfile.mojo",       # name='mojo'
    ],
    cache_repo="user/cache-repo",
)

python -m scripts.cli compose \
    layers/Containerfile \
    layers/Containerfile.scientific \
    layers/Containerfile.mojo \
    --repo user/cache-repo

python -m scripts.cli compose \
    --name base:weird-named-file.txt \
    --name mojo:other-file.txt \
    weird-named-file.txt other-file.txt

python -m scripts.cli restore Containerfile.mojo --name mojo
# Cache tag becomes 'layer-mojo-<hash>' instead of 'layer-<hash>'.
# Omit --name to keep the old back-compat tag for existing callers.

source /path/to/container-layer/scripts/uv_shim.sh /path/to/Containerfile

layer.build_and_push()  # Execute, snapshot, upload

# Skills
FETCH github:oaustegard/claude-skills /mnt/skills/user

# Python environment
RUN uv pip install --system pandas numpy requests

# Path config
RUN echo '/mnt/skills/user/remembering' > /usr/local/lib/python3.12/dist-packages/muninn-remembering.pth

# Custom setup
ENV MY_VAR=hello
WORKDIR /home/claude

© oaustegard, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 13 other files (scripts) in container-layer of oaustegard/claude-skills.

• SKILL.md
• CHANGELOG.md
• Containerfile
• README.md
• boot-ccotw.sh
• boot.sh
• scripts/__init__.py
• scripts/__main__.py
• scripts/cli.py
• scripts/containerfile.py
• scripts/layer_cache.py
• scripts/test_baseline_paths.py
• scripts/test_named_layers.py
• scripts/uv_shim.sh

Open the folder on GitHubat commit 6fc82b8

Used in 1 other repository

We found 2 copies of this SKILL.md (exact, near-identical or edited) in other folders, from 1 other GitHub owner. This page covers the copy in oaustegard/claude-skills, which our catalogue first saw on October 7, 2026.

• majiayu000/claude-skill-registryskills/bash/container-layer