probuilder

Unity Open MCP — ProBuilder Extension

Skill for AI agents driving Unity ProBuilder in a project through the unity-open-mcp MCP server.

This domain is embedded in the bridge and opt-in. Its tools compile in only when the project has com.unity.probuilder installed (the bridge sets the UNITY_OPEN_MCP_EXT_PROBUILDER define automatically). Its tool group is hidden from ListTools until the connected session activates it.

Preconditions

• Unity Editor is open with the target project.
• unity_open_mcp_ping returns connected: true.
• The project has com.unity.probuilder installed. If capabilities reports the probuilder group as available: false, install the package and let the bridge recompile.
• The probuilder tool group is activated — call unity_open_mcp_manage_tools(action="activate", group="probuilder") before invoking any probuilder_* tool. Fresh sessions start with two default-on groups (core and gate-and-verify); activate the other groups you need on demand.
• The Unity project has com.unity.probuilder available.

Tool prefix

All tools in this pack use unity_open_mcp_probuilder_*. Mutating tools target a scene GameObject — every mutator runs the full gate path with paths_hint scoped to the host's scene path; the read-only tool (probuilder_get_mesh_info) is gate-free.

Face selection: indices vs direction

Every face-targeting tool (extrude, delete_faces, set_face_material) accepts either:

• face_indices: [0, 2, 4] — explicit indices. Pass them if you have called get_mesh_info and know exactly which faces you want.
• face_direction: "Up" — semantic selection by face normal. One of Up / Down / Left / Right / Forward / Back.

Passing both returns conflicting_selection. Passing neither returns missing_parameter. Out-of-range indices return invalid_face_indices (with the offending values and the valid range). Direction selection uses a ~45° tolerance — faces whose normal is close to the axis are included; faces that match no axis are bucketed under other in get_mesh_info.