MuJoCo Viewer for VS Code

A live 3D viewer and editor for MuJoCo MJCF models, built into VS Code.

Open an MJCF .xml file and get a real-time physics simulation alongside your code. Edit attributes in the XML and watch the scene update. Click anything in the 3D view to inspect and tweak it, and have your changes flow back into the XML as undoable edits.

Preview release. Feedback and bug reports welcome at github.com/julien-blanchon/mujoco-viewer/issues.

What it is

A workbench for iterating on MuJoCo robot models. The usual loop when writing MJCF is edit XML → run a separate viewer → squint at a compile error → re-edit. This extension collapses that into a single VS Code window: the XML and the running simulation sit side by side, and everything round-trips automatically.

On the viewer side

• Live physics — the simulation runs in-panel. Play, pause, step, or reset. Physics is real MuJoCo (the official mujoco-js WASM build), not a visual approximation.
• Full 3D navigation — orbit with the mouse, WASD / arrow keys to fly, F to re-frame, right-click to pan. Tunable in settings.
• Scene understanding — a tree of bodies, joints, geoms, cameras, lights, materials, textures, tendons, actuators, sensors, and keyframes. Click anything to select and inspect.
• Viewpoints — jump to any MJCF-declared <camera>, or click "track body" to follow a moving part through the simulation.
• Debug overlays — contact points, contact forces, center-of-mass markers, inertia boxes, joint frames, tendon paths, perturbation arrows — all toggleable.
• Screenshots — save a PNG of the current frame with one command.

On the editor side

• Two-way editing — type in the XML and the simulation re-compiles on the fly. Drag a gizmo on a body, change a value in the inspector, apply a keyframe — the XML is updated through WorkspaceEdit, so it's all undoable in the regular text editor.
• Compile errors surfaced as toasts — MuJoCo rejects a malformed edit and you see the exact message in the viewer. No context-switching to a terminal.
• Multi-file models — <include> graphs resolve transparently. Meshes (STL / OBJ / MSH), textures (PNG / HDR / custom builtins), and heightfields load from the workspace automatically.
• Inspector edits — change a body's position, swap a geom's material, re-arrange a keyframe, toggle a light — the inspector panel maps every field directly onto its attribute in the source XML.
• Save semantics match VS Code — the viewer marks documents dirty, Cmd/Ctrl+S persists, closing a dirty tab prompts. Nothing surprising.

On the simulation side

• Standard MuJoCo features — constraints, contact dynamics, actuators, tendons, sensors, flexcomps, all work out of the box.
• Keyframes — MJCF <keyframe> entries appear in the tree; click to apply, edit fields in the inspector to modify.
• Perturbation — drag a body in the running simulation to apply a test force.
• Fixed time step — the viewer honours your MJCF's <option timestep=…>.

Install

1. Install the extension from the Marketplace (search MuJoCo Viewer).
2. Open any MJCF .xml file (anything with <mujoco> as the root element).
3. Run MuJoCo: Open with MuJoCo Viewer from the command palette, or click the viewer icon in the editor title bar.

Models included with MuJoCo (humanoid, cassie, shadow hand, etc.) all work out of the box.

Make it open by default

You can have MuJoCo files open in the viewer automatically instead of the text editor. Set mujoco-viewer.editor.defaultViewer:

Naming convention

The cleanest setup is to name your MuJoCo models humanoid.mjcf.xml or humanoid.mujoco.xml. With mjcfOnly, only those files open in the viewer by default — plain .xml keeps its normal behaviour — and the XSD schema registers for them automatically.

Schema validation

If you install Red Hat XML (free, widely-used) and name your files *.mjcf.xml or *.mujoco.xml, the MuJoCo schema auto-registers and you get in-editor autocomplete and validation — no xsi:noNamespaceSchemaLocation needed on your <mujoco> root.

Element and attribute completion:

Enum completion on constrained attributes:

Inline validation:

If you'd rather keep the plain .xml suffix, run XML: Bind to Grammar/Schema File… from the Red Hat XML command palette and point it at https://raw.githubusercontent.com/julien-blanchon/mujoco-schema/main/mujoco_schema.xsd.

Schema registration is on by default — turn it off via mujoco-viewer.model.schemaValidation.

Commands

Playback keybindings only fire while a viewer tab is focused and the text editor is not — Space / R / F stay safe to type normally.

Settings

All settings live under mujoco-viewer.* and update live — no reload needed.

• Simulation — autoPlay, pauseOnFileChange
• Camera — flySpeed, boostMultiplier, slowDivisor, invertY
• Rendering — shadows, showGrid, showSkybox, backgroundStyle
• Editor — openBehavior (replace vs. side-by-side), defaultViewer (see above)
• Panels — defaultCollapsed (useful on small screens)
• Model — schemaValidation (gates the Red Hat XML registration above)
• Screenshot — directory (default save folder; blank = prompt each time)
• Developer — logLevel for the MuJoCo Viewer output channel

Requirements

• VS Code 1.100 or newer
• Optional: Red Hat XML — only needed for in-editor MJCF autocomplete and validation. The viewer itself works without it.

Privacy

No telemetry. The extension and all physics computation run locally — no network requests except for optional schema lookups when you explicitly reference a remote XSD.

License

MIT. The bundled MuJoCo WASM is Apache-2.0 via mujoco-js.

Links

• Source: github.com/julien-blanchon/mujoco-viewer
• Issues: github.com/julien-blanchon/mujoco-viewer/issues
• MuJoCo: mujoco.org · documentation