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 hamzabellouch/agent-skills --skill center-massgit clone --depth 1 https://github.com/hamzabellouch/agent-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/hamzabellouch/agent-skills/center-mass)<a href="https://agentmods.dev/skills/hamzabellouch/agent-skills/center-mass"><img src="https://agentmods.dev/badge/skills/hamzabellouch/agent-skills/center-mass/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/hamzabellouch/agent-skills/center-mass"><img src="https://agentmods.dev/badge/skills/hamzabellouch/agent-skills/center-mass.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 | $0.00029 | $0.00325 |
| Opus 5.5 | $0.00012 | $0.00130 |
| Sonnet 5.5 | $0.00006 | $0.00065 |
| Haiku 4.5 | $0.00003 | $0.00032 |
Grade A, and why
center-mass 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 7d 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
Center of Mass
ID: mech.momentum.center_of_mass
Domain: Mechanics → Momentum
Difficulty: 2/5
Prerequisites
- mech.momentum.conservation
Core Concepts
- center of mass
- CM frame
- reduced mass
- CM motion
Key Equations
$$ \vec R_{CM} = \frac{1}{M}\sum_i m_i\vec r_i $$ $$ \vec F_{ext} = M\ddot{\vec R}_{CM} $$ $$ \mu = \frac{m_1 m_2}{m_1+m_2} $$
Methods
- Compute CM for discrete and continuous systems
- Switch to CM frame to simplify collisions
- Use reduced mass for two-body problems
Typical Problem Types
- CM of a composite body
- Two-body collision in CM frame
- Rocket staging
Common Pitfalls
- Confusing CM with geometric centroid
- Forgetting reduced mass in two-body problems
Related Skills
- mech.momentum.conservation
- rel.general.two_body
References
- Kleppner & Kolenkow Ch.4
- Goldstein Ch.1
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.
- 7d ago First seen · 58 lines · 29 tokens per session scan A eb81bb903b6f
center-mass is a skill published in the GitHub repository hamzabellouch/agent-skills (8 stars, last pushed today), licensed MIT. It adds 29 tokens to every session and 325 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 2026-10-10.
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