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 randommonicle/claude-skills --skill skill-library-buildergit clone --depth 1 https://github.com/randommonicle/claude-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/randommonicle/claude-skills/skill-library-builder)<a href="https://agentmods.dev/skills/randommonicle/claude-skills/skill-library-builder"><img src="https://agentmods.dev/badge/skills/randommonicle/claude-skills/skill-library-builder/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/randommonicle/claude-skills/skill-library-builder"><img src="https://agentmods.dev/badge/skills/randommonicle/claude-skills/skill-library-builder.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 | $0.00141 | $0.02430 |
| Opus 5 | $0.00071 | $0.01215 |
| Sonnet 5 | $0.00028 | $0.00486 |
| Haiku 4.5 | $0.00014 | $0.00243 |
Grade A, and why
skill-library-builder 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 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.
Enumerates other installed skillslowAgent snooping
Other skills' SKILL.md files reveal prompts, capabilities and secrets that should be invisible to peers.
| Unslop scanners installed | `ls ~/.claude/skills \| grep unslop` | `unslop-text`, `unslop-code`, `unslop-ui` | Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
How it starts
The opening of the file, as written. The whole thing — 132 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Skill library builder
Turn a repository into a project-specific skill library: what the system is, what must not break, how it is set up, run and tested, how it fails, how to prove a fix is real, and how to change it safely. The output is a set of focused runbooks under .claude/skills/, not generic documentation. Reject any skill that only restates the README.
This skill is the method behind the PropOS library (16 skills authored by Fable, reviewed by Sonnet and a domain reviewer, fixed by Opus, on 2026-07-02). The PropOS artefacts docs/PLAN_fable_skill_library.md and docs/FABLE_PROMPT_skill_library.md are a full worked instance of everything below.
When this applies
Load this when the task is to build or refresh a library of operating knowledge for a repository, especially before a knowledgeable engineer leaves, when onboarding, or when a codebase needs to be workable by a cheaper model. Do not load it to author one skill on a subject you already understand: write that directly. Do not load it to change product code: this is a read-and-author job.
Non-negotiables
- Discover before you author. No skill is written until its facts are verified against the repo.
- Write only under the skills root (
.claude/skills/). The rest of the repo is read-only unless the user explicitly asks for code changes. - Ground truth only. Verify every command, flag, path and claim against the repo before stating it. Do not invent commands, flags, paths, ownership, history or success claims. Label inference as inference.
- Verify provenance with git, not memory. Dates, PR and commit numbers, and "who added what when" are the claims most likely to be wrong. Confirm each with
git log --follow <path>orgit show <sha>before writing it. This is the single most common authoring error: the technical facts (function names, config keys, error codes) verify cleanly while the story of when and why a thing landed drifts, especially when two similar artefacts exist. - Do not route around the project's change-control. Nothing you write may tell a reader to bypass the project's gates.
- Do not present candidate work as proven. Open, deferred or experimental items stay labelled open.
- Put volatile facts behind re-verification commands and date-stamp them.
- No mutating git and no side effects. Forbidden without explicit authorisation:
reset,checkout,switch,clean,commit,push,pull,merge,rebase, publish, deploy, and any database or production write.
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 · 132 lines · 141 tokens per session scan A 4f33931c3c35
skill-library-builder is a skill published in the GitHub repository randommonicle/claude-skills (23 stars, last pushed 3d ago), licensed Apache-2.0. It adds 141 tokens to every session and 2,430 once invoked, about $0.0007 per session on Opus 5. A static security scan graded it A with 1 finding (enumerates other installed skills). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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