Host as static files

Play is a static web app. Any static host (GitHub Pages, Nginx, S3 + CDN, …) works as long as a few requirements are met.

MIME types

These must be correct, otherwise the browser will refuse to load modules/WASM:

  • .mjs / .js → text/javascript; charset=utf-8

  • .wasm → application/wasm

If you see Worker or module load failures, check the response Content-Type in DevTools Network.

CORS

If forgeBase= points to a different origin, the forge host must allow CORS for:

  • mujoco.js

  • mujoco.wasm

  • version.json (optional but recommended)

If you move built-in environment preset assets to another origin via envAssetBase= or PLAY_ENV_ASSET_BASE, that host must also allow CORS for the HDRI/EXR files.

Caching

For development, it’s often safest to disable caching (Cache-Control: no-store) to avoid confusing stale Worker/module behavior.

The local dev server (tools/dev_server.py) is intentionally dev-biased:

  • it serves .mjs/.js/.wasm with Cache-Control: no-store (so you never run old code by accident), and

  • it disables conditional caching for ESM/WASM (always returns a 200 with a body).

This makes reloads and model switching appear slower in local dev, because the browser cannot reuse cached modules/WASM.

Play itself is cache-friendly by default:

  • it does not add a cb=... cache-bust query unless you explicitly set cacheBust=always.

For production/demo hosting, do the opposite: prefer immutable URLs (pin forge by commit SHA) and serve with long-lived caching headers (ideally immutable).

version.json is optional. Play may fetch it with no-store for diagnostics when verbose/perf logging is enabled, but it is not required for correct caching.

Environment preset assets follow the same model: by default they come from the repo-local assets/env/ directory, but you can point them at a shared CDN or object store with envAssetBase= (or PLAY_ENV_ASSET_BASE in site_config.js). If those remote files fail to load, Play keeps the preset lighting and falls back to the existing cached/gradient environment path rather than failing the viewer.

The included dev server is a good reference implementation: tools/dev_server.py.