100% in the browser
No installs, no Docker, no Python env to break. Open a tab and start working.
Visual robot design and physics simulation
Open a tab.
Build a robot.
Run the physics. Iterate.
Quickly visualize and edit your robot's physical properties with real-time physics in the browser.
No install · No account · Files stay local
Why Critter Engine
Build faster without moving your workflow into a black box.
Files stay yours
No accounts required. Your robots, scenes, and projects live in your browser and your local files.
See what your model is doing
Stop hunting through XML for a wrong number. Quickly visualize bodies, joints, sites, collisions, tendons, and inertias. Mistakes are obvious the moment you load the file, and you can fix them on the spot.
Built on MuJoCo
For the MuJoCo workflow.
Critter Engine is built on MuJoCo. If you already work in MuJoCo, Critter Engine fits your stack without locking you in.
Real MuJoCo physics
Running natively in your browser.
Import standard MJCF/XML models with meshes
Critter Engine parses them and gives you a visual handle on every body, joint, tendon, constraint, inertial, mesh, collision, and more. Edit in just a few clicks.
Export your edited model
Save clean MJCF/XML you can drop into any MuJoCo runtime.
Familiar robot library
Franka Panda and FR3, UR5e and UR10e, KUKA iiwa, Boston Dynamics Spot, Unitree Go2/G1/H1, Agility Cassie, Agilex Piper, and more, plus grippers and hands.
Full MuJoCo sensor support
IMUs, force/torque, touch, joint and actuator state, tendons, and the rest.
What you can do with Critter Engine
Design, inspect, drive, and export robot models visually.
Catch bugs at a glance
Toggle overlays for collisions, sites, joint axes, tendons, and inertias. Click to inspect and edit.
Compose without typing
Drag in robots, grippers, props, and terrain, or build from scratch. Visually tune every part of a robot's physics model.
Drive the robot
Move any joint with a live slider. Watch the actuators respond in real time, with or without physics running.
See what the robot sees
Mount a virtual camera on any body, preview the live feed, snapshot stills, and record video clips of the simulation.
Run real-time physics in the browser
Press play and watch the constraints do their job. Press stop and your scene returns to exactly where it started.
Save and share
Export your project as a single portable file and reopen it anywhere.
FAQ
Practical answers before launch.
Where is my data stored?
Locally. Your files live in your browser, your downloads folder, and nowhere else. Optional caching of uploaded meshes between sessions is opt-in. Cloud storage is coming soon, and will also be opt-in.
Do I need an account?
No.
What browsers are supported?
The latest two versions of Chrome, Edge, Firefox, and Safari.
Can I import an existing model?
Yes. Import MJCF/XML with meshes, edit visually, export it back out.
Does Critter Engine train policies?
Not yet. Today it's focused on design and simulation. Training is on the roadmap.
Is it free?
Yes. The in-browser editor is the heart of the product and we intend to keep it free. Any future cloud or team features would be optional paid add-ons.
Critter Engine
Stop debugging robots in a text editor.
No install · No account · Files stay local