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 NTCoding/claude-skillz --skill writing-testsgit clone --depth 1 https://github.com/NTCoding/claude-skillzWrote 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/ntcoding/claude-skillz/writing-tests)<a href="https://agentmods.dev/skills/ntcoding/claude-skillz/writing-tests"><img src="https://agentmods.dev/badge/skills/ntcoding/claude-skillz/writing-tests/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/ntcoding/claude-skillz/writing-tests"><img src="https://agentmods.dev/badge/skills/ntcoding/claude-skillz/writing-tests.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 | $0.00076 | $0.02230 |
| Opus 5.5 | $0.00030 | $0.00892 |
| Sonnet 5.5 | $0.00015 | $0.00446 |
| Haiku 4.5 | $0.00008 | $0.00223 |
Grade C, and why
writing-tests scanned grade C with 1 finding 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 1mo 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.
Hidden instructionshighPrompt injection
Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.
- [ ] Unicode: emojis 👨👩👧👦, RTL text, combining characters - [ ] Special characters: quotes, backslashes, null bytes - [ ] SQL/HTML/script injection patterns - [ ] Leading/trailing whitespace - [ ] Mixed case sens The source is not reproduced here
No licence file
A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.
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.
- 1mo ago First seen · 277 lines · 76 tokens per session scan C 22cdc78cd42e
writing-tests is a skill published in the GitHub repository NTCoding/claude-skillz (356 stars, last pushed 7mo ago), with no licence file. It adds 76 tokens to every session and 2,230 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it C with 1 finding (hidden instructions). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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