Agent skill

Benchmark Packing

by coreos in coreos/chunkah

Benchmark chunkah packing algorithm changes against a series of OCI images.

Apache-2.0Auto-check passedDevOps & Cloud

Install Benchmark Packing

skills CLI
$ npx skills add coreos/chunkah --skill benchmark-packing -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install coreos/chunkah benchmark-packing --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/coreos/chunkah.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/benchmark-packing .claude/skills/benchmark-packing && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
benchmark-packing
GitHub stars
148
Token cost
~1.1k tokens
SKILL.md length
388 words
Files
1
Skills in repo
4
Repo updated
First seen
Licence
Apache-2.0

At a glance

Benchmark chunkah packing algorithm changes against a series of OCI images.

  • Works in 6 steps: Build chunkah → Prepare source images → Chunk the series → …
  • Tasks that involve Containers
  • SKILL.md covers Overview, Pipeline, Comparing multiple… and Pitfalls
  • Calls podman and just

What it does

Benchmark Packing is an agent skill from coreos/chunkah. Benchmark chunkah packing algorithm changes against a series of OCI images.

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in DevOps & Cloud, covering Containers. The repository describes itself as: An OCI building tool for content-based layers. The licence is Apache-2.0.

When your agent uses it

  • Tasks that involve Containers

Example prompts

  • “/benchmark-packing”

Requirements

  • Docker

Workflow steps

6 steps, taken from the step headings in SKILL.md.

  1. Build chunkah
  2. Prepare source images
  3. Chunk the series
  4. Analyze layer reuse
  5. Clean up chunked images
  6. Compare against original packing

What it can do on your machine

Read from SKILL.md and the folder at commit 780bcd2. 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

    Shell commands in SKILL.md call:

    • podman
    • just

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

  • Network

    No URLs in SKILL.md.

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

  • Credentials

    Names no API keys, tokens, secrets or passwords.

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

Context cost

Benchmark Packing loads about 1.1k tokens when it runs. Until then it costs about 23 tokens; SKILL.md has 388 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~23
When it runs · the whole SKILL.md, loaded when a task matches
~1.1k

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

Auto-check passed

The automated check found no risky patterns in SKILL.md.

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); files beside SKILL.md are not scanned.

SKILL.md

The full file from coreos/chunkah at commit 780bcd2, republished under its Apache-2.0 licence (© coreos). 388 words, ~1,050 tokens.

Download SKILL.mdSave it as .claude/skills/benchmark-packing/SKILL.md (or your agent's skills folder).
name
benchmark-packing
description
Benchmark chunkah packing algorithm changes against a series of OCI images.

Benchmark Packing

Overview

This skill guides benchmarking of packing algorithm changes by chunking a series of consecutive OCI images and measuring layer reuse between them. The key tools are:

  • tools/chunk-image-series.py -- chunks a series of images
  • tools/analyze-layer-reuse.py -- compares layer sharing across the chunked series

Pipeline

1. Build chunkah

After making code changes, build the container image:

bash
just buildimg --no-chunk

This produces localhost/chunkah:latest.

2. Prepare source images

Source images must be in containers-storage. Either:

From OCI archives:

bash
for archive in /path/to/*.ociarchive; do
    version=$(echo "${archive}" | grep -oP 'PATTERN')
    skopeo copy "oci-archive:${archive}" "containers-storage:localhost/myrepo:${version}"
done

From a registry:

chunk-image-series.py can pull directly from a registry:

bash
tools/chunk-image-series.py docker://quay.io/fedora/fedora-coreos \
    --tag-filter '43.*' --limit 10 ...
3. Chunk the series
bash
tools/chunk-image-series.py containers-storage:localhost/myrepo \
    --tag-filter '43.*' \
    --prefix myrepo-chunked \
    --chunkah-image localhost/chunkah \
    --force \
    -- --prune /sysroot --max-layers 128

Key flags:

  • --force to overwrite results from prior runs
  • --limit N to control how many images to process
  • Extra chunkah args go after --
4. Analyze layer reuse

Pass all chunked images as separate positional arguments:

bash
image_args=()
for i in $(seq 0 9); do
    image_args+=("containers-storage:localhost/myrepo-chunked:${i}")
done
tools/analyze-layer-reuse.py --json "${image_args[@]}" > results.json

IMPORTANT: do NOT use brace expansion inside quotes (e.g. "...:{0,1,2}") -- it won't expand. Always build the argument list explicitly.

The JSON summary fields are:

  • avg_reuse_ratio -- fraction of data shared (0.0 to 1.0)
  • avg_download_bytes -- average new data per update
5. Clean up chunked images

Always clean up chunked images after capturing results:

bash
for i in $(seq 0 9); do
    podman rmi "localhost/myrepo-chunked:${i}" 2>/dev/null || true
done
6. Compare against original packing

Always measure the original (un-chunked) images as a baseline:

bash
image_args=()
for tag in $(podman images --filter reference='localhost/myrepo' \
    --format '{{.Tag}}' | sort); do
    image_args+=("containers-storage:localhost/myrepo:${tag}")
done
tools/analyze-layer-reuse.py --json "${image_args[@]}" > original.json

Comparing multiple configurations

To compare a code change against the current defaults:

  1. Chunk with the baseline chunkah (quay.io/coreos/chunkah:dev)
  2. Capture and save JSON results
  3. Clean up chunked images
  4. Build local chunkah with your changes
  5. Chunk with localhost/chunkah
  6. Capture and save JSON results
  7. Clean up chunked images
  8. Compare the two JSON files

The source images and original baseline can be reused across runs.

Show full SKILL.md (133 more words)Show less

Pitfalls

Duplicate tags

chunk-image-series.py creates temporary localhost/tmp-chunk-src tags during chunking. These are cleaned up on exit, but if a prior run was interrupted, stale tags may remain and cause duplicate entries. Before running analysis, verify tags are clean:

bash
podman images --filter reference='localhost/myrepo' --format '{{.Tag}}' | sort

If you see duplicate tags, remove them before proceeding. A red flag in results is min_download_bytes: 0 -- this means two consecutive images were identical (likely duplicates).

Sample size sensitivity

Results can vary significantly depending on the specific time window of builds tested. Always test against multiple independent corpora (e.g. different image types, different time periods) before concluding a change is beneficial. An improvement on one sample may not generalize.

Layer count matters

The default --max-layers is 64. Results at 64 layers vs 128 layers can differ substantially. Always compare configurations at the same layer count.

© coreos, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/benchmark-packing of coreos/chunkah.

Open the folder on GitHubat commit 780bcd2

Compare with similar skills

Benchmark Packing next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Benchmark Packing compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Benchmark Packing this skillcoreos/chunkah148—~1.1kAutomated safety check: PassApache-2.0
Iron Proxy Gateway for NanoClawnanocoai/nanoclaw31k—~4.6kAutomated safety check: NotesMIT
GreptimeDB Dev Docker ImageGreptimeTeam/greptimedb6.7k—~4kAutomated safety check: NotesApache-2.0
Senior DevOps Toolkitmaslennikov-ig/claude-code-orchestrator-kit2596 repos~1.1kAutomated safety check: NotesCustom licence
LangBot Deployment Guidelangbot-app/LangBot18k—~1.2kAutomated safety check: NotesApache-2.0
Build Openshell Mxc WindowsNVIDIA/OpenShell15k—~4.9kAutomated safety check: PassApache-2.0

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Categories

Questions about Benchmark Packing

What does Benchmark Packing do?

Benchmark chunkah packing algorithm changes against a series of OCI images. Benchmark Packing is an agent skill from coreos/chunkah. Benchmark chunkah packing algorithm changes against a series of OCI images.

When should I use Benchmark Packing?

Benchmark Packing fits situations like: tasks that involve Containers.

How do I install Benchmark Packing in Claude Code?

Run `npx skills add coreos/chunkah --skill benchmark-packing -a claude-code`. Or copy the skill folder (.agents/skills/benchmark-packing in coreos/chunkah) into .claude/skills/benchmark-packing in your project. Claude Code loads it when a task matches its description.

How do I install Benchmark Packing in Codex?

Run `npx skills add coreos/chunkah --skill benchmark-packing -a codex`. Or copy the skill folder (.agents/skills/benchmark-packing in coreos/chunkah) into .agents/skills/benchmark-packing in your project. Codex loads it when a task matches its description.

Can I use Benchmark Packing in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add coreos/chunkah --skill benchmark-packing -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/benchmark-packing, .gemini/skills/benchmark-packing, .github/skills/benchmark-packing and .opencode/skills/benchmark-packing in your project.

What does Benchmark Packing need to run?

Going by SKILL.md and its folder, Benchmark Packing needs the command-line tools its instructions call (podman and just). Our summary lists: Docker.

Does Benchmark Packing access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Benchmark Packing safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Benchmark Packing use?

Benchmark Packing is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Benchmark Packing use?

About 1.1k tokens (SKILL.md is roughly 4.2k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Benchmark Packing?

Skills that share tags, products or a category with Benchmark Packing: Iron Proxy Gateway for NanoClaw (nanocoai/nanoclaw, 31k stars), GreptimeDB Dev Docker Image (GreptimeTeam/greptimedb, 6.7k stars), Senior DevOps Toolkit (maslennikov-ig/claude-code-orchestrator-kit, 259 stars) and LangBot Deployment Guide (langbot-app/LangBot, 18k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Benchmark Packing?

coreos (a GitHub organization) maintains it in coreos/chunkah, which has 148 GitHub stars. The repository holds 4 skills in this directory. The repository was last updated on October 5, 2026.

Source: coreos/chunkah on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.