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 054-design-tddgit 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/054-design-tdd)<a href="https://agentmods.dev/skills/jabrena/plinth/054-design-tdd"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/054-design-tdd/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/054-design-tdd"><img src="https://agentmods.dev/badge/skills/jabrena/plinth/054-design-tdd.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 | $0.00093 | $0.00803 |
| Opus 5 | $0.00046 | $0.00402 |
| Sonnet 5 | $0.00019 | $0.00161 |
| Haiku 4.5 | $0.00009 | $0.00080 |
Grade A, and why
054-design-tdd 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 10d 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 — 73 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development Design
Guide Java developers through Test-Driven Development for implementation work. This is an interactive SKILL.
What is covered in this Skill?
- Maintaining or refining a list of candidate test cases
- Selecting the next useful behavior or test case before editing production code
- Writing a failing test first to clarify the public interface, API shape, or usage of the code
- Writing only enough functional production code to pass the selected test
- Refactoring new and existing code while tests remain green
- Adding newly discovered test cases to the list without losing the current TDD cycle
- Reporting skipped checks, missing tests, and remaining risks when verification is incomplete
Constraints
Keep implementation work inside the red-green-refactor cycle, with one selected behavior driving each small change.
- MUST read
references/054-design-tdd.mdbefore applying TDD guidance - MUST maintain or refine a test list when more than one behavior, edge case, or question is in scope
- MUST select the next useful behavior or test case before writing production code
- MUST write or describe the failing test first and use it to clarify the public interface or usage
- MUST implement only the functional production code needed to pass the selected failing test
- MUST refactor new and existing code only after the selected test passes and while keeping tests green
- MUST report skipped checks, missing tests, and remaining risks when verification is incomplete
When to use this skill
- Apply TDD
- Use test-driven development
- Drive this Java change with tests
- Write the failing test first
- Red-green-refactor this feature
- Build this behavior test first
Workflow
- Build the Test List
Read references/054-design-tdd.md, then list candidate behaviors, edge cases, error paths, integration boundaries, and design questions that may need tests. Add newly discovered cases to the list as work proceeds.
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.
- 10d ago First seen · 73 lines · 93 tokens per session scan A 5bd4e89b3d07
054-design-tdd is a skill published in the GitHub repository jabrena/plinth (438 stars, last pushed yesterday), licensed Apache-2.0. It adds 93 tokens to every session and 803 once invoked, about $0.0005 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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