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 dylantarre/animation-principles --skill arc-masterygit clone --depth 1 https://github.com/dylantarre/animation-principlesWrote 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/dylantarre/animation-principles/arc-mastery)<a href="https://agentmods.dev/skills/dylantarre/animation-principles/arc-mastery"><img src="https://agentmods.dev/badge/skills/dylantarre/animation-principles/arc-mastery/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/dylantarre/animation-principles/arc-mastery"><img src="https://agentmods.dev/badge/skills/dylantarre/animation-principles/arc-mastery.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk 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 | $0.00028 | $0.00897 |
| Opus 5 | $0.00014 | $0.00449 |
| Sonnet 5 | $0.00006 | $0.00179 |
| Haiku 4.5 | $0.00003 | $0.00090 |
Grade A, and why
arc-mastery 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 9d 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 — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arc Mastery
The Natural Path Principle
Almost all natural movement follows curved paths. Arms swing in arcs. Heads turn on arcs. Thrown objects travel parabolic arcs. When animation moves in straight lines, it immediately feels mechanical and artificial. Arcs are the signature of organic motion.
Core Theory
Anatomical basis: Bodies are systems of hinges and pivots. When a joint rotates, everything attached to it moves in an arc centered on that joint. Straight lines require mechanical rails—biology doesn't have those.
Physics basis: Gravity creates parabolic curves on projectiles. Momentum creates curved paths when direction changes. Straight-line direction changes require infinite force.
Arc Types
Circular arcs: Pure rotation around a single pivot (pendulum, door swing) Parabolic arcs: Projectile motion under gravity (jumps, throws) S-curves: Complex motion through multiple pivots (whip crack, spine movement) Figure-8 patterns: Continuous flowing motion (hips during walk, flowing cloth)
The Pivot Chain
Understanding arcs requires understanding pivot hierarchies:
- Shoulder rotates → elbow travels an arc
- Elbow rotates → wrist travels a compound arc
- Wrist rotates → fingertips travel triple-compound arcs
Each joint adds complexity to the motion path of everything downstream.
Interaction with Other Principles
Follow through follows arcs: Appendages settle along curved paths, not straight returns.
Anticipation creates arc initiation: The wind-up often establishes the arc's direction.
Timing affects arc perception: Fast motion through arcs needs exaggerated curves to read clearly.
Overlapping action creates offset arcs: Secondary elements trace their own arc patterns behind the primary.
Domain Applications
UI/Motion Design
- Page transitions: Elements should enter/exit on curved paths, not straight slides
- Menu expansions: Items fan out on arcs from origin point
- Gesture responses: Swipe follow-through curves naturally
- Notification entries: Slight arc on slide-in prevents robotic feel
- Dragging: Release trajectories should curve based on velocity vector
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.
- 9d ago First seen · 89 lines · 28 tokens per session scan A 6d3b1d4b6086
arc-mastery is a skill published in the GitHub repository dylantarre/animation-principles (81 stars, last pushed 8mo ago), licensed MIT. It adds 28 tokens to every session and 897 once invoked, about $0.0001 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 2026-09-03.
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