.urdf  →  .xml

URDF to MJCF

Convert a robot description from URDF to MJCF in the browser. Nothing is installed and nothing is queued: the file is read, written in the other format, and handed back with a list of anything that could not be carried across.

Convert a file

URDF .urdf MJCF .xml

Drop your URDF here

Drop the folder too if the model references meshes.

Files are read on our server and deleted after a day. Nothing is published.

What this conversion costs

These are the things MJCF has no place for. They are reported on the converted file as well, as a comment at the top, so the file itself says what is missing from it.

  • Joint velocity limits. MJCF does not keep a velocity limit on the joint — MuJoCo enforces speed through actuators, so the number moves there or disappears.
  • Named materials. Colours survive; the material name a URDF shares between links does not.

A URDF has no ground and no gravity

It describes one robot, floating, and what you get back is that robot: links, joints, geometry, inertia — plus a free base if it has legs, because a legged robot welded to the origin can neither stand up nor fall over. The floor, the lights and the solver settings are not in a URDF to begin with, so they are yours to add. The physics lab supplies its own.

Meshes are referenced, not embedded

MuJoCo wants its meshes in a directory it can find. The file we hand back points at meshes/, so keep the folder next to it.

Collision geometry is what gets simulated

If a link has visual geometry only, MuJoCo has nothing to collide with there. The check on the viewer page lists those links before you find out the hard way.

The two formats

URDF .urdf
the ROS description of a robot: links, joints, geometry and inertia, one rigid tree. A URDF file, line by line
MJCF .xml
MuJoCo's own format: the same robot, plus everything a solver needs to simulate it. MJCF, explained

Converting is rarely the whole job. Once you have the MJCF, the viewer shows what actually came across — collision geometry against visual, joint limits, where the mass sits — and the physics lab answers the question a file cannot: whether the robot stands up when gravity is switched on.

Other directions