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 me2resh/apexyard --skill c4git clone --depth 1 https://github.com/me2resh/apexyardWrote 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/me2resh/apexyard/c4)<a href="https://agentmods.dev/skills/me2resh/apexyard/c4"><img src="https://agentmods.dev/badge/skills/me2resh/apexyard/c4/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/me2resh/apexyard/c4"><img src="https://agentmods.dev/badge/skills/me2resh/apexyard/c4.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 2 findings, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium MCP Rug Pull · line 254 npx commands without a version suffix (e.g. @1.0.0) create a rug-pull risk if the upstream server is compromised and publishes a malicious update.Fix: Pin the version: npx @scope/[email protected]
- medium MCP Rug Pull · line 340 Docker image references without a specific tag (:latest is implicit) or digest (@sha256:...) can be silently replaced by a malicious image.Fix: Pin the image: image:tag or image@sha256:abc123
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 | $0.00041 | $0.05845 |
| Opus 5.5 | $0.00016 | $0.02338 |
| Sonnet 5.5 | $0.00008 | $0.01169 |
| Haiku 4.5 | $0.00004 | $0.00585 |
Grade A, and why
c4 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 4d 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 — 387 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Writing: read docs/skills/shared/writing-rule.md before you write a durable artifact.
/c4 — Generate C4 Architecture Diagrams
Reads the target project's codebase and produces filled-in Level 1 (System Context) and Level 2 (Container) diagrams as Mermaid markdown. Saves the slog of filling in the templates by hand for a repo you already understand structurally.
This skill complements /handover (which seeds a stub L2 once at onboarding). Use /c4 whenever the architecture changes substantially and the diagrams need a refresh — or for a project that wasn't onboarded via /handover.
For projects that hit Mermaid's ceiling — L3 (component) precision, auto-zoom across levels, tags/perspectives — pass --dsl to emit a Structurizr DSL workspace instead. See "Escape hatch: Structurizr DSL (L3+)" below.
Path resolution
Read the registry path via portfolio_registry, the per-project docs dir via portfolio_projects_dir, and the ideas backlog via portfolio_ideas_backlog — all from .claude/hooks/_lib-portfolio-paths.sh. Source the helper at the top of any bash block that touches those paths:
source "$(git rev-parse --show-toplevel)/.claude/hooks/_lib-read-config.sh"
source "$(git rev-parse --show-toplevel)/.claude/hooks/_lib-portfolio-paths.sh"
registry=$(portfolio_registry)
Defaults match today's single-fork layout (./apexyard.projects.yaml, ./projects, ./projects/ideas-backlog.md). Adopters in split-portfolio mode override the portfolio.{registry, projects_dir, ideas_backlog} keys in .claude/project-config.json. Don't hardcode literal apexyard.projects.yaml or projects/ paths in bash blocks — the helper resolves whichever mode the adopter is in. See docs/multi-project.md.
Usage
/c4 # current cwd, both levels
/c4 sample-app # registered project, both levels
/c4 sample-app --level=1 # only the L1 system-context diagram
/c4 . --level=2 # only the L2 container diagram for cwd
/c4 sample-app --force # overwrite existing diagrams
/c4 sample-app --dsl # Structurizr DSL escape hatch (L3+), instead of Mermaid
/c4 sample-app --dsl --force # overwrite an existing workspace.dsl
What ships with it
2 files 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.
- 4d ago Changed · -2 lines 69853fbf9ff2
- 11d ago Changed 681531f1967b
- 1mo ago Changed · +4 lines 06b12948cbf3
- 1mo ago First seen · 385 lines · 41 tokens per session scan A 689a6e7ed951
c4 is a skill published in the GitHub repository me2resh/apexyard (533 stars, last pushed today), licensed MIT. It adds 41 tokens to every session and 5,845 once invoked, about $0.0002 per session on Opus 5.5. 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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