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 slow-in-out-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/slow-in-out-mastery)<a href="https://agentmods.dev/skills/dylantarre/animation-principles/slow-in-out-mastery"><img src="https://agentmods.dev/badge/skills/dylantarre/animation-principles/slow-in-out-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/slow-in-out-mastery"><img src="https://agentmods.dev/badge/skills/dylantarre/animation-principles/slow-in-out-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 | $0.00030 | $0.00981 |
| Opus 5 | $0.00015 | $0.00491 |
| Sonnet 5 | $0.00006 | $0.00196 |
| Haiku 4.5 | $0.00003 | $0.00098 |
Grade A, and why
slow-in-out-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 — 92 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Slow In / Slow Out Mastery
The Physics Principle
Objects in the real world don't move at constant speeds—they accelerate from rest and decelerate to stops. Slow in/slow out (also called ease in/ease out) captures this fundamental truth. Without it, animation looks mechanical. With it, motion feels alive.
Core Theory
Slow Out (Ease Out): More drawings clustered at the start of a movement. The object accelerates away from its starting position gradually.
Slow In (Ease In): More drawings clustered at the end of a movement. The object decelerates into its final position gradually.
Linear motion: Equal spacing between positions. Rare in nature, useful for mechanical elements or stylistic choice.
The Spacing Principle
Traditional animators controlled this through drawing spacing:
- Tight spacing = slow movement (drawings close together)
- Wide spacing = fast movement (drawings far apart)
Digital animators control this through easing curves—mathematical functions that describe how values change over time.
Common Easing Functions
- Ease Out: Fast start, slow end (70% of UI animations)
- Ease In: Slow start, fast end (exits, departures)
- Ease In Out: Slow start and end (elegant, deliberate)
- Linear: Constant rate (mechanical, looping)
- Custom bezier: Precise control for specific feels
Interaction with Other Principles
Timing is modified by easing: The same duration feels different with different easing. Ease out feels faster than ease in at identical durations.
Anticipation often uses ease in: The wind-up accelerates before the fast action.
Follow through uses ease out: Settling motion decelerates to rest.
Squash/stretch intensity follows easing: More deformation during fast phases, less during slow phases.
Domain Applications
UI/Motion Design
- Page transitions: Ease out for entrances (fast appearance, settle), ease in for exits
- Modals: Ease out scale-up for friendly, non-jarring appearance
- Buttons: Ease out on press feedback (immediate response, smooth settle)
- Loading: Linear for progress bars (predictable), ease for spinners (organic)
- Hover states: Quick ease out to start, ease in out for smooth feel
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 · 92 lines · 30 tokens per session scan A b5056e08ec77
slow-in-out-mastery is a skill published in the GitHub repository dylantarre/animation-principles (81 stars, last pushed 8mo ago), licensed MIT. It adds 30 tokens to every session and 981 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 2026-09-03.
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