μLottie

μLottie (or micro Lottie) is an ahead-of-time compiler for the Lottie file format.

It takes a Lottie JSON and emits a JavaScript module with a tiny runtime to evaluate it.

See the EXPLAINER.md to understand the original motivations.

Status: proof of concept. Never released, no programatic API yet. AI is largely involved. Kinda vibe, still heavy steering by human. They keep working state on HANDOFF.md, for how it works and what is left.

Try it

The entire compiler is fully available on the browser. You can see it from the demo page.

Or to try it locally, see ulottie-dev-server for instructions.

Compiler Usage

cargo run -p ulottie-compiler -- --help

Layout

• ulottie-compiler/: the compiler (serde -> IR -> payload -> scene → JS)
• ulottie-compiler/runtime/: the runtime, as JS modules
• ulottie-dev-server/: compile server, test suites, and the demo page
• _fixtures/animations/: Lottie fixtures to track coverage

Tests

cargo nextest run --features eval       # 87 tests
yarn workspace ulottie-dev-server test  # 157 tests

The second spawns the compile server itself, drives a real browser, and pixel-diffs every fixture against lottie-web. Both must stay green.

License

MIT