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 iliaal/whetstone --skill ia-c-systemsgit clone --depth 1 https://github.com/iliaal/whetstoneWrote 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/iliaal/whetstone/ia-c-systems)<a href="https://agentmods.dev/skills/iliaal/whetstone/ia-c-systems"><img src="https://agentmods.dev/badge/skills/iliaal/whetstone/ia-c-systems/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/iliaal/whetstone/ia-c-systems"><img src="https://agentmods.dev/badge/skills/iliaal/whetstone/ia-c-systems.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 | $0.00084 | $0.01017 |
| Opus 5.5 | $0.00034 | $0.00407 |
| Sonnet 5.5 | $0.00017 | $0.00203 |
| Haiku 4.5 | $0.00008 | $0.00102 |
Grade A, and why
ia-c-systems scanned grade A 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 17d 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
| `goto cleanup` / `goto err` | Kernel, OpenSSL, curl, php-src: the dominant multi-resource release idiom | How it starts
The opening of the file, as written. The whole thing — 71 lines — stays where its author put it; the contents beside it link to each section on GitHub.
C Systems & Native Code
Covers C11 and later for libraries, systems code, and native extensions. For C++ (RAII, templates, move semantics), see the ia-cpp-systems skill.
Working rules
- Preserve the repository's sanctioned idioms and ABI; do not turn a scoped fix into a restyle.
- State ownership, check fallible calls, validate public boundaries, and assert internal invariants.
- Preserve recovery outside optimizer assumptions. An assertion that becomes an assumption can remove the branch handling its false case. Keep recoverable checks as runtime branches with diagnostic-only assertions behind a debug preprocessor guard. Exercise the fallback in an optimized release build.
- Guard staged initialization against reentry. Set an in-progress marker before callback-capable work on every constructor or factory path. Permit retry after failure only after fully releasing and resetting partial state. Test recursive entry and retry after failed initialization.
- Bound traversal of external input and check sizes before allocation or narrowing.
- Choose helpers only when they name a concept, own an error, or isolate a side effect.
- Verify the actual rebuilt artifact; use instrumented tests for safety and representative release builds for performance.
Repo conventions outrank this skill
Read the repo's AGENTS.md/CLAUDE.md, its public headers, and two adjacent .c files before writing anything. Where they conflict with the rules below, they win, and the diff carries no note about it.
Do not skip this gate. Established C codebases sanction idioms these rules would otherwise flag:
| Local idiom | Where it is correct |
|---|---|
| Tab indentation | php-src and its extensions, Linux kernel |
goto cleanup / goto err |
Kernel, OpenSSL, curl, php-src: the dominant multi-resource release idiom |
Macros containing return |
RETURN_*/RETVAL_* in PHP extensions, Py_RETURN_* in CPython |
| Project status types | zend_result, CURLcode, int plus errno: do not invent a parallel enum beside one |
What ships with it
8 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.
- 17d ago Changed · +4 lines 22bb1ce76001
- 1mo ago Changed 5b1fbcb6df3a
- 1mo ago Changed · -136 lines e52c7c71de1a
- 1mo ago First seen · 203 lines · 84 tokens per session scan A 1b936dc4293c
ia-c-systems is a skill published in the GitHub repository iliaal/whetstone (35 stars, last pushed today), licensed MIT. It adds 84 tokens to every session and 1,017 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-07.
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