SUPPORTED PATH
URDF can enter MuJoCo's parser and be serialized into native XML.
01URDF→
02MuJoCo parser→
03mjSpec / compiled model→
04MJCF serialization→
05Target review
The saved MJCF can look structurally different because MuJoCo has compiler semantics, defaults and native constructs that do not map one-to-one to URDF source structure.
REVIEW
Opening successfully is not the same as preserving intent.
Kinematics
Review body nesting, joint ordering and any composite-joint assumptions.
Inertials
Check mass and inertia values after compiler-side normalization or inference.
Contacts + friction
MuJoCo owns simulator-native contact semantics beyond basic URDF structure.
Actuation
URDF joints do not automatically define the MJCF actuator model you want.
Sensors / tendons
Native MJCF constructs need explicit target-side modeling where required.
Provenance
Keep the source URDF and conversion configuration beside the target derivative.