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 jabrena/plinth --skill 053-design-simple-rulesgit clone --depth 1 https://github.com/jabrena/plinthWrote 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/jabrena/plinth/053-design-simple-rules)<a href="https://agentmods.dev/skills/jabrena/plinth/053-design-simple-rules"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/053-design-simple-rules/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/jabrena/plinth/053-design-simple-rules"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/053-design-simple-rules.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00675 |
| Opus 5 | $0.00043 | $0.00338 |
| Sonnet 5 | $0.00017 | $0.00135 |
| Haiku 4.5 | $0.00009 | $0.00068 |
Grade A, and why
053-design-simple-rules 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 9d 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 — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Simple Design Rules
Guide Java developers through Kent Beck's simple design rules when evaluating design and refactoring choices. This is an interactive SKILL.
What is covered in this Skill?
- Using tests as the first correctness boundary before design cleanup
- Revealing intention and maximizing clarity before abstraction pressure
- Reducing duplication without hiding domain meaning or worsening readability
- Treating fewer elements as the final simplification pressure after correctness, clarity, and duplication
- Comparing Java design and refactoring options with the ordered rules
- Reporting the chosen option, tradeoffs, validation signal, and remaining risk
Constraints
Apply simple design rules in priority order, and do not optimize later rules by weakening earlier rules.
- MUST read
references/053-design-simple-rules.mdbefore applying the rules - MUST evaluate the rules in this order: passes the tests, reveals intention, has no duplication, has the fewest elements
- MUST treat passing tests as the correctness boundary before design cleanup
- MUST prefer clear intention over abstraction for its own sake
- MUST reduce duplication only when the result preserves or improves clarity
- MUST consider fewer elements only after correctness, clarity, and duplication have been addressed
When to use this skill
- Apply simple design rules
- Use Beck's simple design rules
- Review this design with simple design rules
- Choose between these refactoring options
- Keep this Java design simple
- Does this design pass the simple design rules?
Workflow
- Anchor Correctness
Read references/053-design-simple-rules.md, then identify the behavior under discussion and the tests, characterization checks, build checks, or manual evidence that define whether the code works.
- Reveal Intention
Evaluate whether names, types, responsibilities, control flow, API shape, and test descriptions make the domain decision clear to a future maintainer.
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.
- 9d ago First seen · 67 lines · 86 tokens per session scan A 26b029d5e587
053-design-simple-rules is a skill published in the GitHub repository jabrena/plinth (437 stars, last pushed today), licensed Apache-2.0. It adds 86 tokens to every session and 675 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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