# mesh_set_surface_material

Assign a Material (res:// path) to a MeshInstance3D (undoable). Default surface -1 sets 'material_override' (whole instance); a surface index >= 0 sets that surface's override material (must be within the mesh's surface count). Refuses a non-MeshInstance3D node or a non-Material resource.

Agent View of the PolicyLayer registry record for `mesh_set_surface_material`. HTML page: https://policylayer.com/tools/breakpoint-mcp/mesh-set-surface-material

## Facts

- Tool: `mesh_set_surface_material`
- Server: Breakpoint (`breakpoint-mcp`) — https://policylayer.com/tools/breakpoint-mcp.md
- Install: `npx -y breakpoint-mcp`
- Homepage: https://www.npmjs.com/package/breakpoint-mcp
- Risk category: Write (Medium risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 3 (2 required)
- Recommended policy verdict: Rate-limited

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `path` | string | yes | MeshInstance3D node path relative to the scene root |
| `surface` | integer | no | Surface index, or -1 (default) for material_override |
| `material_path` | string | yes | Material resource res:// path (StandardMaterial3D / ShaderMaterial / …) |

Parameters from the server's own tool schema.

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "mesh_set_surface_material",
    "arguments": {
      "path": "<path>",
      "material_path": "<material_path>"
    }
  }
}
```

## Why mesh_set_surface_material is rated Medium

This tool creates or modifies rendering state (material assignment) on a 3D node without permanently deleting data or executing arbitrary code. While it affects visual output, the change is reversible (undoable) and is a direct property modification rather than code execution. Write is the appropriate category as it modifies object properties in a reversible manner.

From the tool's own definition: "Tool description states it 'Assign[s] a Material... to a MeshInstance3D (undoable)', indicating it modifies graphics rendering state by setting material overrides on mesh surfaces. The word 'undoable' confirms the action is reversible."

Risk signals: Accepts file system path (path)

## Use case

AI agents use mesh_set_surface_material to create or update resources in Breakpoint, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Breakpoint environment.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Breakpoint:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "mesh_set_surface_material": {
      "limits": [
        {
          "counter": "mesh_set_surface_material_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Breakpoint (273)

- `anim_delete` — Destructive — https://policylayer.com/tools/breakpoint-mcp/anim-delete.md
- `anim_remove_key` — Destructive — https://policylayer.com/tools/breakpoint-mcp/anim-remove-key.md
- `filesystem_move` — Destructive — https://policylayer.com/tools/breakpoint-mcp/filesystem-move.md
- `gd_rename` — Destructive — https://policylayer.com/tools/breakpoint-mcp/gd-rename.md
- `inputmap_erase_action` — Destructive — https://policylayer.com/tools/breakpoint-mcp/inputmap-erase-action.md
- `mp_wire_rpc` — Destructive — https://policylayer.com/tools/breakpoint-mcp/mp-wire-rpc.md
- `node_delete` — Destructive — https://policylayer.com/tools/breakpoint-mcp/node-delete.md
- `project_remove_autoload` — Destructive — https://policylayer.com/tools/breakpoint-mcp/project-remove-autoload.md
- `resource_save` — Destructive — https://policylayer.com/tools/breakpoint-mcp/resource-save.md
- `resource_set_import_settings` — Destructive — https://policylayer.com/tools/breakpoint-mcp/resource-set-import-settings.md
- `runtime_node_remove` — Destructive — https://policylayer.com/tools/breakpoint-mcp/runtime-node-remove.md
- `runtime_peer_stop` — Destructive — https://policylayer.com/tools/breakpoint-mcp/runtime-peer-stop.md
- `scene_close` — Destructive — https://policylayer.com/tools/breakpoint-mcp/scene-close.md
- `scene_reload` — Destructive — https://policylayer.com/tools/breakpoint-mcp/scene-reload.md
- `shader_set_code` — Destructive — https://policylayer.com/tools/breakpoint-mcp/shader-set-code.md
- `tilemap_clear` — Destructive — https://policylayer.com/tools/breakpoint-mcp/tilemap-clear.md
- `vcs_restore` — Destructive — https://policylayer.com/tools/breakpoint-mcp/vcs-restore.md
- `vcs_stash` — Destructive — https://policylayer.com/tools/breakpoint-mcp/vcs-stash.md
- `cs_dbg_attach` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-attach.md
- `cs_dbg_continue` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-continue.md
- `cs_dbg_launch` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-launch.md
- `cs_dbg_restart` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-restart.md
- `cs_dbg_set_breakpoints` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-set-breakpoints.md
- `cs_dbg_set_exception_breakpoints` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-set-exception-breakpoints.md
- `cs_dbg_set_variable` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-set-variable.md
- `cs_dbg_step` — Execute — https://policylayer.com/tools/breakpoint-mcp/cs-dbg-step.md
- `dbg_attach` — Execute — https://policylayer.com/tools/breakpoint-mcp/dbg-attach.md
- `dbg_continue` — Execute — https://policylayer.com/tools/breakpoint-mcp/dbg-continue.md
- `dbg_data_breakpoints` — Execute — https://policylayer.com/tools/breakpoint-mcp/dbg-data-breakpoints.md
- `dbg_goto` — Execute — https://policylayer.com/tools/breakpoint-mcp/dbg-goto.md
- …and 243 more: https://policylayer.com/tools/breakpoint-mcp.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=breakpoint-mcp · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/breakpoint-mcp