animation-editor

animation-editor is a skill for Claude Code from vchelaru/FlatRedBall2. It costs 0 tokens per session (2,692 once invoked), scanned A, original, MIT.

A guide to the FlatRedBall2 desktop editor for editing .achx animation-chain files, including its project location and two-panel layout. Avalonia is the desktop user-interface framework used by this rewritten version of the editor.

In plain words
What is it for?
Use it when locating the editor, changing its animation or preview UI, understanding .achx files, or deciding which related testing and documentation guidance applies.
Why use it?
It helps developers work on the current editor instead of accidentally changing the older Windows Forms version in another repository. It also points to separate guidance for editor tests, screenshots, and browser checks.

Skill for Claude Code

Written for Claude Code: installed under .claude/.

Install

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.

agentmods
npx agentmods add skills/vchelaru/flatredball2/animation-editor
Any agent
npx skills add vchelaru/FlatRedBall2 --skill animation-editor
Clone the repo
git clone --depth 1 https://github.com/vchelaru/FlatRedBall2

Made for: Claude Code.

Wrote 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.

agentmods badge for animation-editor

README.md
[![agentmods](https://agentmods.dev/badge/skills/vchelaru/flatredball2/animation-editor.svg)](https://agentmods.dev/skills/vchelaru/flatredball2/animation-editor)
Your own site
<a href="https://agentmods.dev/skills/vchelaru/flatredball2/animation-editor"><img src="https://agentmods.dev/badge/skills/vchelaru/flatredball2/animation-editor.svg" alt="Measured on agentmods" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,692 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00000 $0.02692
Opus 5 $0.00000 $0.01346
Sonnet 5 $0.00000 $0.00538
Haiku 4.5 $0.00000 $0.00269

Measured yesterday against content hash 27d5174141dd, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

animation-editor 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 yesterday.

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.

.claude/skills/animation-editor/SKILL.md · 113 lines

How it starts

The opening of the file, as written. The whole thing — 113 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Animation Editor — Location & Layout

The Animation Editor is the desktop tool that lets users edit .achx animation chain files (frames, regions, shapes, onion-skinning, preview playback). It is being rewritten on top of Avalonia and lives inside this repository at:

tools/AnimationEditorAvalonia/

The legacy WinForms version (FlatRedBall.AnimationEditorForms) lives in the separate FlatRedBall (FRB1) repo at FRBDK/FlatRedBall.AnimationEditorForms/. Do not edit it for FRB2 issues — that codebase is being replaced. Issues filed in vchelaru/FlatRedBall2 always refer to the Avalonia version.

For writing tests against the editor — headless Avalonia, service wiring, the [AvaloniaFact] deadlock pitfall — see the animation-editor-testing skill. For generating headless documentation screenshots of the UI, see the animation-editor-screenshots skill. For WASM/?demo= visual proof in the browser host, see animation-editor-browser-verify.

.achx is a general-purpose format — the editor authors, runtimes interpret

.achx is not an FRB2 file. It is a general-purpose animation/atlas format consumed by several runtimes that each render it their own way: Gum (across its Skia, raylib, and sokol.net backends), MonoGame/KNI/FNA, FRB1 (custom-shader rendering), and FRB2 (SpriteBatch). The editor authors the format; each runtime decides what to do with the data. This frames every feature decision here:

  • A field the editor exposes does not obligate any runtime to apply it. Store the data in the format; whether a given runtime renders it is that runtime's choice. Do not gate adding a frame field on FRB2 (or any single runtime) implementing it — e.g. per-frame Red/Green/Blue are authored and stored for game code to consume, while FRB2's SpriteBatch path never applies them itself.
  • The preview is a reference rendering, not a per-runtime contract. The bottom panel renders with SkiaSharp (PreviewControl, SKCanvas/SKColorFilter in DrawFrameCore), so it will diverge from what a MonoGame/FNA/FRB1 runtime produces for the same file. That divergence is inherent to a general-purpose tool and is not a bug — pick a sensible canonical interpretation. "The preview might not match a runtime" is never a reason to withhold an authoring feature.

Read the full file on GitHub · 113 lines

Changes

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.

  1. yesterday First seen · 113 lines · 0 tokens per session scan A 27d5174141dd

Subscribe to this mod's changes

animation-editor is a skill published in the GitHub repository vchelaru/FlatRedBall2 (14 stars, last pushed today), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 2,692 tokens. 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 2026-09-04.

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