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 FacturaScripts/fs-claude-plugin --skill extension-developergit clone --depth 1 https://github.com/FacturaScripts/fs-claude-pluginWrote 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/facturascripts/fs-claude-plugin/extension-developer)<a href="https://agentmods.dev/skills/facturascripts/fs-claude-plugin/extension-developer"><img src="https://agentmods.dev/badge/skills/facturascripts/fs-claude-plugin/extension-developer/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/facturascripts/fs-claude-plugin/extension-developer"><img src="https://agentmods.dev/badge/skills/facturascripts/fs-claude-plugin/extension-developer.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 | $0.00033 | $0.00195 |
| Opus 5.5 | $0.00013 | $0.00078 |
| Sonnet 5.5 | $0.00007 | $0.00039 |
| Haiku 4.5 | $0.00003 | $0.00019 |
Grade A, and why
extension-developer 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 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.
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.
What it actually says
Desarrollo de extensiones
Usa como instrucciones de especialidad el perfil ../../agents/extension-developer.md y léelo completo antes de actuar.
Ejecución portable
- En Claude Code, delega al agente nativo
extension-developercuando esté disponible. - En Codex, aplica el perfil directamente o pásalo a un subagente genérico para una tarea acotada cuando resulte útil.
- Si no puedes delegar, realiza tú mismo el trabajo siguiendo el perfil.
- Consulta
fs-dev:docs-experty el código que se va a extender para confirmar hooks y firmas.
Implementa siempre desde Extension/; no modifiques Core/ ni el plugin extendido.
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 Changed · -54 lines · -158 tokens per session f3a4197092d0
- 1mo ago First seen · 72 lines · 191 tokens per session scan A ac31bd800f77
extension-developer is a skill published in the GitHub repository FacturaScripts/fs-claude-plugin (10 stars, last pushed 10d ago), licensed MIT. It adds 33 tokens to every session and 195 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-08-31.
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