Stims

Play and live-edit MilkDrop presets in your browser.

The original .milk files by Geiss, Rovastar, Flexi, Eo.S., Martin and ~130 more authors. Point them at any audio, change the equations while they play, and share what you see as a link.

▶ Open toil.fyi

Stims lives at toil.fyi. Any WebGL2 browser; no account, no install.

Play → edit → share. This preview is accelerated; watch the 25-second workflow at recorded speed. The capture is silent.

The clips are silent. Each one opens its preset live, and a click on the page turns the sound on.

• Play a 1,787-preset catalog of the originals, curated picks first. Presets stay .milk files: there is no conversion step, and export gives you .milk back.
• Edit while it plays, as MilkDrop 2 let you. The source opens in an editor with completions and compiler diagnostics; zoom, warp, rot and decay are sliders. When an equation drives one, the slider and the code that sets it name the audio that reaches it (eq · bass, zoom=… ← bass), read from the equations.
• Point it at anything: a browser tab, a YouTube link, your microphone, a local file, or the built-in demo loop.
• Send a link. The address bar is the session, and whoever opens it needs nothing installed: every bundled preset's code fits in the link — edits and remix lineage included — and one click turns the sound on.
• Perform with it. WebMIDI learn maps knobs and faders to controls (mappings persist per device), a cue monitor crossfades between two running presets, and a chromeless projector window mirrors the stage to a second display.
• Calm by default. Nothing plays until you start audio, one action stops everything, and motion follows your system's reduce-motion setting.

Why "Stims"? It's built for stimmers as much as for MilkDrop fans: the sensory controls let you decide how much happens on screen and when it stops. MilkDrop presets can flash. Presets measured as frequent flashers carry a warning, and Settings → Reduce flashing hides them; most presets haven't been measured yet.

How it compares

Butterchurn and projectM are the renderers most people embed or run today. Stims is a whole app, on a renderer of its own.

	Stims	Butterchurn	projectM
What it is	A browser app you open	A JS renderer you embed	A native library and player
Presets	.milk files, as-is	Converted to JSON first	.milk files
Editing	Live editor with diagnostics and sliders	None built in	None built in
Flashing safety	Flash audit against WCAG 2.3.1, live governor, brightness ceiling and motion dampener	None built in	None built in
Finding presets	Search, collections, previews, favorites, history, links	Up to the host app	Playlist files

How close to MilkDrop is it? A CI test compiles all 1,750 presets in the bundled Butterchurn pack — a different population from the 1,787-preset catalog above — for both WebGL2 and WebGPU. None is unsupported on either, and 1,578 run with no approximation on both; the other 172 approximate a shader on WebGPU or use a name the expression VM doesn't know (the test). Matching projectM pixel for pixel is a stricter check, made one preset at a time against native projectM captures, and it covers only a few presets so far (results, method). If a preset looks wrong, report it; that is the most useful help there is.

The full comparison says which one to pick for what.

What's new here

Playing MilkDrop presets in a browser isn't new: Butterchurn did it first. Neither is the live editor, which brings back what MilkDrop 2 had built in. These three are:

• Per-pixel equations run on the GPU. On WebGPU, per-pixel and custom-wave equations compile into the shader and run for every vertex at once; that covers 1,094 of the 1,102 catalog presets with per-pixel code. Butterchurn and projectM run them on the CPU, one grid point at a time. Seeded differential fuzz tests hold the GPU, the JIT and the interpreter to the same results. Their first runs found 18 shipped preset blocks the JIT couldn't compile and divergent results in 32% of GPU-lowered programs.
• Fidelity is measured against native projectM. Both renderers are stepped on a fixed clock, and a difference counts only when it exceeds that preset's own run-to-run noise. Every result is published per preset, passing or not (scoreboard), and promotion refuses a reference that a blank frame would pass.
• The corpus is analysed as programs. bun run lab:dataflow reads which audio reaches each control and each drawn program from the equations alone, and the editor shows the same reading beside each slider. In 73 of 2,679 presets, the audio reaches nothing on screen. Used as training data, the corpus shows presets behave as threshold programs: gradient-boosted trees beat every network tried, and 41% of memoryless audio-driven controls come back as exact equations from their behaviour (findings).

How it works

Part	What it does	Code
Compiler and VM	Parses preset equations (EEL2) into an IR and runs them on an interpreter or a JIT, lowering per-pixel equations into the shader on WebGPU; translates preset shaders to GLSL and WGSL	packages/milkdrop-toolchain/src/compiler/, src/js/milkdrop/vm.ts
Renderer	WebGL2 is the baseline; an optional WebGPU path falls back to it when a preset needs something WebGPU can't run yet	src/js/milkdrop/
Audio	FFT, bands and transients computed in an AudioWorklet, packed into a GPU texture	src/js/core/audio-handler.ts, packages/audio-reactive/src/
App	The React workspace: browsing, the editor, and the URL as session state	src/js/frontend/
Edge (optional)	Cloudflare Worker routes for model-backed preset generation, blending and visual search; playback and editing don't need them	functions/

Technical foundations has the system diagram and what each part has proven so far, the architecture overview follows one frame through the code, and the docs index has the rest.

Quick start

You need Bun 1.4.4+ and a browser with WebGL2. WebGPU is optional.

git clone https://github.com/zz-plant/stims.git
cd stims
bun install
bun run dev

Then open http://localhost:5173. The git history is large: git clone --filter=blob:none https://github.com/zz-plant/stims.git skips its old binaries and clones much faster. To change code, follow the contributor setup, which adds the quality gate and the browser the browser-backed tests need.

Use the compiler without the app

The compiler is a plain module, so scripts and CI can check .milk files the same way the live editor does:

// compile.ts — print the errors the editor would show
import { readFileSync } from 'node:fs';
import { compileMilkdropPresetSource } from './packages/milkdrop-toolchain/src/compiler.ts';

const { diagnostics } = compileMilkdropPresetSource(
  readFileSync(process.argv[2] ?? '', 'utf8'),
);
for (const d of diagnostics.filter((d) => d.severity === 'error')) {
  console.log(`${d.line ?? '?'}: ${d.message}`);
}

bun compile.ts public/milkdrop-presets/eos-glowsticks-v2-03-music.milk

To learn the equation language, start with the authoring curriculum; bun run lab:dataflow -- --preset <id> reports which audio signals reach each control of any catalog preset.

Standalone packages

Four parts of Stims are standalone packages under packages/: the app imports them, they have no dependency on the app, and each has a read-only mirror repository, a demo site and an npm-ready build. eel-conformance, flash-guard and milkdrop-toolchain are on npm at 0.1.0, with 0.1.1 merged and not yet published; audio-reactive is not published and stays a workspace package. Publishing has the release state and steps.

The corpus also does stewardship work outside this repository: butterchurn and eel-wasm both have open PRs that adopt eel-conformance as their engine's test suite (butterchurn#108, eel-wasm#66), and the ns-eel2 source audit pins what MilkDrop 2's expression language actually does, cited from the C source MilkDrop ships.

Package	What it is
milkdrop-toolchain	The parser, EEL2 interpreter and JIT, IR, HLSL analysis with GLSL emission, EEL-to-WGSL lowering, formatter and MilkDrop 2 exporter above, as an npm package.
eel-conformance	An executable specification of the preset expression language: 82 portable JSON cases any MilkDrop implementation can run.
flash-guard	The WCAG 2.3.1 flash analysis behind the catalog's flash warnings, and the live governor behind Reduce flashing.
audio-reactive	The AudioWorklet FFT, harmonic/percussive separation, beat tracking and reactivity metrics behind the audio path.

Verification commands

bun run check:quick   # lint, types and repo guards; no tests (under a minute)
bun run check         # full checks, package suites, unit + compatibility + corpus
bun run test          # default: unit + compatibility
bun run check:all     # full checks and all profiles, including browser e2e
bun run build         # production bundle

Help out

The most useful things, roughly in order of effort:

• Tell us when a preset looks wrong. Use Share to preserve edited source, then include the link, browser, backend, audio source, and steps to reproduce. A matching MilkDrop or projectM screenshot helps compare output: report a preset that renders wrong.
• Share presets and finds in Discussions: a preset you wrote or restored, a collection worth curating, a song that makes one sing. The remix thread collects one-equation edits of a featured preset.
• Send code. Start with CONTRIBUTING.md; docs/ONBOARDING.md maps the codebase and says which parts are hard. The good first issues are scoped small on purpose. Compatibility changes should bring a test and its evidence.

What changed recently is in the changelog.

For audio, editing, and sharing, start with the user guide; the docs index links current references and historical evidence.

For recording or streaming, start with the OBS setup recipe. It covers a Browser Source demo, regular-browser capture, and separate audio routing; native OBS verification is still pending.

Acknowledgments and lineage

Stims depends on work by:

• Ryan Geiss, who wrote MilkDrop, the Winamp plugin, and the per-frame and per-pixel equation language presets are written in.
• Jordan Berg (jberg) and the Butterchurn contributors, who first ran MilkDrop presets in WebGL and whose preset parsing Stims learned from.
• Carmelo Piccione, Mischa Spiegelmock, and the projectM maintainers, whose C++ implementation is the reference Stims measures itself against.
• The MilkDrop preset authors, who wrote the 1,787 presets in the catalog. The most-credited handles in the shipped catalog, counting every appearance in an accretive credit chain rather than only solo bylines, are Geiss, Flexi, Martin, Rovastar, Eo.S., Stahlregen, Unchained, fiShbRaiN, Phat, Aderrasi, Shifter, Zylot, ORB, suksma, Cope, Goody, and Krash — alongside roughly 120 more.
• Nullsoft, whose Winamp is where MilkDrop ran.

Stims is an independent implementation. MilkDrop, Butterchurn, and projectM are credited as creative and technical lineage; no official affiliation is implied. See Lineage and Credits.

Licensed under the Unlicense — public domain.