URL parameters

Play is configured primarily via URL query parameters. Parameters are parsed on the main thread and (for backend-relevant knobs) propagated to the Worker.

This page is end-user focused and documents the most commonly-used knobs.

Boolean tokens

For boolean parameters, Play accepts these (case-insensitive):

• true: 1, true, yes, on

• false: 0, false, no, off

For verbose logging, log=debug is also accepted.

Parameters

Key	Type	Default	Scope	Notes
model	string	builtin default	main → worker (load)	MJCF path under model/ (or local_model/ for local-only files) or a builtin alias (e.g. raj, cards).
forgeBase	string (URL)	(auto)	main → worker	Base URL for forge dist/<ver>/ (must contain mujoco.js and mujoco.wasm). If omitted, the Worker uses a local dev layout.
ver	string	site_config.js (PLAY_VER)	main → worker	MuJoCo/forge dist version token. Used to expand {ver} in the default forge base template (/forge/dist/{ver}/), and forwarded to the Worker for diagnostics.
plugins	string list	empty	main	Comma-separated ESM import specifiers/URLs. Each entry is imported via dynamic import(). Relative specifiers (.//../) resolve relative to the repo root (same folder as index.html).
embed	bool	false	main	Embed mode for iframe/container hosting. Play sizes to the parent container instead of forcing a 100vh shell. Runtime behavior and default panel visibility stay unchanged.
theme	string	dark	main	Initial UI theme. Supported values: dark and light.
font	string	100	main	Initial UI font scale preset. Supported values: 50, 75, 100, 150, 200 (percent presets matching the built-in font selector).
envAssetBase	string (URL)	repo-local assets/env/	main	Base URL for built-in environment preset assets such as preset-sun / preset-moon HDRI or EXR files. Relative values resolve from the repo/web root. This only changes where preset env assets are loaded from; it does not affect forge dist/.

Developer/debug parameters

Play also supports additional developer/debug URL parameters (strict mode, verbose logs, renderer debugging, tick-rate clamps, etc). To keep this page user-focused, those knobs are documented under Runtime configuration.

One commonly-used debug knob:

• cacheBust=always: forces cache-busting (adds cb=...) for the Worker URL and forge resource URLs. Default is cache-friendly (no cb).

Deprecated / reserved parameters

These are recognized by the runtime but are currently deprecated, internal, or have no user-facing effect:

• mode=...: deprecated and ignored (Play is Worker-only).

• cb=...: internal cache-bust parameter (only used when cacheBust=always is enabled).

• hide / dump / find / hide_big / big_n / big_factor / hide_index: parsed by the legacy param parser but not currently applied.