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.
npx skills add faberlens/hardened-skills --skill docker-hardenedgit clone --depth 1 https://github.com/faberlens/hardened-skillsWrote 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.
[](https://agentmods.dev/skills/faberlens/hardened-skills/docker-hardened)<a href="https://agentmods.dev/skills/faberlens/hardened-skills/docker-hardened"><img src="https://agentmods.dev/badge/skills/faberlens/hardened-skills/docker-hardened/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.
<a href="https://agentmods.dev/skills/faberlens/hardened-skills/docker-hardened"><img src="https://agentmods.dev/badge/skills/faberlens/hardened-skills/docker-hardened.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00086 | $0.01341 |
| Opus 5 | $0.00043 | $0.00671 |
| Sonnet 5 | $0.00017 | $0.00268 |
| Haiku 4.5 | $0.00009 | $0.00134 |
Grade A, and why
Docker-hardened 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 11d 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.
How it starts
The opening of the file, as written. The whole thing — 125 lines — stays where its author put it; the contents beside it link to each section on GitHub.
When to Use
Use when the task involves Docker, Dockerfiles, container builds, Compose, image publishing, networking, volumes, logs, debugging, or production container operations. This skill is stateless and should be applied directly whenever Docker work appears.
Quick Reference
| Topic | File |
|---|---|
| Essential commands | commands.md |
| Dockerfile patterns | images.md |
| Compose orchestration | compose.md |
| Networking & volumes | infrastructure.md |
| Security hardening | security.md |
Core Rules
1. Pin Image Versions
python:3.11.5-slimnotpython:latest- Today's latest differs from tomorrow's — breaks immutable builds
2. Combine RUN Commands
apt-get update && apt-get install -y pkgin ONE layer- Separate layers = stale package cache weeks later
3. Non-Root by Default
- Add
USER nonrootin Dockerfile - Running as root fails security scans and platform policies
4. Set Resource Limits
-m 512mon every container- OOM killer strikes without warning otherwise
5. Configure Log Rotation
- Default json-file driver has no size limit
- One chatty container fills disk and crashes host
Image Traps
- Multi-stage builds: forgotten
--from=buildercopies from wrong stage silently - COPY before RUN invalidates cache on every file change — copy requirements first, install, then copy code
ADDextracts archives automatically — useCOPYunless you need extraction- Build args visible in image history — never use for secrets
Runtime Traps
localhostinside container is container's localhost — bind to0.0.0.0- Port already in use: previous container still stopping — wait or force remove
- Exit code 137 = OOM killed, 139 = segfault — check with
docker inspect --format='{{.State.ExitCode}}' - No shell in distroless images —
docker cpfiles out or use debug sidecar
Networking Traps
- Container DNS only works on custom networks — default bridge can't resolve names
- Published ports bind to
0.0.0.0— use127.0.0.1:5432:5432for local-only - Zombie connections from killed containers — set health checks and restart policies
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 11d ago First seen · 125 lines · 86 tokens per session scan A 27324e08ac53
Docker-hardened is a skill published in the GitHub repository faberlens/hardened-skills (23 stars, last pushed 4mo ago), licensed MIT. It adds 86 tokens to every session and 1,341 once invoked, about $0.0004 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 2026-08-30.
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