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 agentmods add skills/damimartinez/book-skills/c-programming-languagenpx skills add DamiMartinez/book-skills --skill c-programming-languagegit clone --depth 1 https://github.com/DamiMartinez/book-skillsWrote 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/damimartinez/book-skills/c-programming-language)<a href="https://agentmods.dev/skills/damimartinez/book-skills/c-programming-language"><img src="https://agentmods.dev/badge/skills/damimartinez/book-skills/c-programming-language.svg" alt="Measured on agentmods" 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 | $0.00167 | $0.01379 |
| Opus 5 | $0.00084 | $0.00690 |
| Sonnet 5 | $0.00033 | $0.00276 |
| Haiku 4.5 | $0.00017 | $0.00138 |
Grade A, and why
c-programming-language 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 6d 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 — 43 lines — stays where its author put it; the contents beside it link to each section on GitHub.
The C Programming Language (K&R, 2nd Edition)
Apply this skill when writing, reviewing, or debugging C code, or explaining C semantics — grounded in K&R's philosophy that C trusts the programmer completely: no hidden costs, no runtime safety net, and correctness is the programmer's explicit responsibility at every step.
Core concepts
"Trust the programmer" — C deliberately omits bounds checking, garbage collection, and most runtime safety nets, on the premise the programmer knows what they're doing and wants no hidden cost. This means C code that "looks fine" can still be wrong in ways the compiler won't catch — when reviewing C, actively look for what the language won't stop, not just syntax errors.
Pointer/array duality & pointer arithmetic — a[i] is defined as *(a + i); arrays decay to pointers in most expressions, and pointer arithmetic is scaled by the pointee's size automatically. Understanding this equivalence is the key to reading and writing idiomatic C (pointer-walking a buffer instead of indexing, passing arrays as pointer+length). When debugging array/pointer code, mentally rewrite between the two forms to spot off-by-one or scaling errors.
Declarations mirror use (the right-left / "spiral" rule) — A declaration like int *a[10] or int (*a)[10] should be read by working outward from the identifier following C's precedence rules ([] and () bind tighter than *), not left-to-right. When a declaration is confusing (arrays of pointers, pointers to functions, pointers to arrays), decompose it this way rather than guessing — this is the single most common source of "wait, what does this even declare" confusion in C.
Manual memory management & ownership — Every malloc/calloc needs an unambiguous owner responsible for exactly one matching free; there's no garbage collector to fall back on. When reviewing allocation code, explicitly trace: who allocates, who's responsible for freeing, and what happens on every exit path (including error returns) — leaks and double-frees are almost always a broken answer to "who owns this."
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.
- 6d ago First seen · 43 lines · 167 tokens per session scan A 87a4ecb37ea6
c-programming-language is a skill published in the GitHub repository DamiMartinez/book-skills (11 stars, last pushed 1mo ago), licensed MIT. It adds 167 tokens to every session and 1,379 once invoked, about $0.0008 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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