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MuJoCo and Gazebo address adjacent parts of the robotics simulation landscape and can be used together in the same engineering workflow. MuJoCo provides a fast, low-level physics engine focused on articulated dynamics, contacts, and programmatic control, while Gazebo provides a broader robotics simulation environment built around worlds, sensors, plugins, and ROS-centered development patterns.
MuJoCo is commonly used when teams want direct access to simulation internals, optimization-oriented workflows, or reinforcement learning and control experiments built around MJCF models and code-driven tooling. Gazebo is commonly used when teams need a larger robotics simulation environment with SDF worlds, sensor simulation, ROS 2 bridging, and broader system-level testing.
The connection point between them is not a native runtime bridge inside either core product but tooling around model interchange. MuJoCo's own README lists gz-mujoco as a two-way SDFormat to MJCF conversion tool, which shows that practitioners sometimes move models between the two ecosystems instead of treating them as mutually exclusive choices.
This pairing is useful for interoperability and comparative workflows, but it does not eliminate differences between the two tools. Teams still need to manage model conversion, behavior differences across engines, and duplicated validation effort when the same system is maintained in both SDF and MJCF forms.