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 Casper-Studios/casper-marketplace --skill plugin-best-practicesgit clone --depth 1 https://github.com/Casper-Studios/casper-marketplaceWrote 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/casper-studios/casper-marketplace/plugin-best-practices)<a href="https://agentmods.dev/skills/casper-studios/casper-marketplace/plugin-best-practices"><img src="https://agentmods.dev/badge/skills/casper-studios/casper-marketplace/plugin-best-practices.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 | $0.00034 | $0.00284 |
| Opus 5 | $0.00017 | $0.00142 |
| Sonnet 5 | $0.00007 | $0.00057 |
| Haiku 4.5 | $0.00003 | $0.00028 |
Grade A, and why
plugin-best-practices 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 2d 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
Plugin Best Practices
Prefer fine-grained plugins that package one coherent installable capability or body of guidance. Consumers install the plugin as a unit instead of assembling cooperating skills or accepting unrelated functionality.
Treat a plugin as an encapsulation boundary. Like a class in object-oriented programming, it exposes a deliberate public interface while hiding implementation details that consumers do not need to understand or invoke.
A plugin can expose one public skill or several independently useful public skills. Those entry points own consumer-facing outcomes while private skills support them without exposing the internal call graph.
Effective Strategies for Focused Agent-Skill Plugins
Follow the guidelines below. Read each linked reference that applies to the plugin design task.
- Expose public outcomes while keeping implementation skills private.
- Package only the metadata and files that consumers need.
What ships with it
4 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.
- 2d ago Changed · +2 lines · -28 tokens per session c2d6da067c3b
- 7d ago First seen · 24 lines · 62 tokens per session scan A 35fa909d72ee
plugin-best-practices is a skill published in the GitHub repository Casper-Studios/casper-marketplace (12 stars, last pushed 3d ago), licensed MPL-2.0. It adds 34 tokens to every session and 284 once invoked, about $0.0002 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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