# set_material_instance_scalar

Set a scalar parameter on a material instance.

Agent View of the PolicyLayer registry record for `set_material_instance_scalar`. HTML page: https://policylayer.com/tools/jjpxdev-unreal-mcp/set-material-instance-scalar

## Facts

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

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `value` | number | yes | Parameter value |
| `instance_path` | string | yes | Material instance asset path |
| `parameter_name` | string | yes | Scalar parameter name |

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": "set_material_instance_scalar",
    "arguments": {
      "value": 0,
      "instance_path": "<instance_path>",
      "parameter_name": "<parameter_name>"
    }
  }
}
```

## Why set_material_instance_scalar is rated Medium

The tool modifies material instance parameters, which changes asset properties in the Unreal Engine project. This is a write operation that creates or modifies data reversibly - material parameter changes can be undone through the editor's undo system or by setting different values. It does not execute arbitrary code, delete assets, or cause irreversible changes.

From the tool's own definition: "set_material_instance_scalar - sets a scalar parameter on a material instance, modifying material properties"

## Use case

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

## Recommended policy (PolicyLayer)

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

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

## Other tools on Unreal (126)

- `delete_actor` — Destructive — https://policylayer.com/tools/jjpxdev-unreal-mcp/delete-actor.md
- `delete_asset` — Destructive — https://policylayer.com/tools/jjpxdev-unreal-mcp/delete-asset.md
- `delete_material_expression` — Destructive — https://policylayer.com/tools/jjpxdev-unreal-mcp/delete-material-expression.md
- `remove_graph_node` — Destructive — https://policylayer.com/tools/jjpxdev-unreal-mcp/remove-graph-node.md
- `build_cook_run` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/build-cook-run.md
- `build_graph` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/build-graph.md
- `build_plugin` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/build-plugin.md
- `build_target` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/build-target.md
- `call_preset_function` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/call-preset-function.md
- `clean_project` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/clean-project.md
- `compile_blueprint` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/compile-blueprint.md
- `content_audit` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/content-audit.md
- `cook_content` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/cook-content.md
- `execute_console_command` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/execute-console-command.md
- `execute_python` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/execute-python.md
- `generate_lods` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/generate-lods.md
- `package_project` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/package-project.md
- `recompile_material` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/recompile-material.md
- `reinit_niagara_system` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/reinit-niagara-system.md
- `render_sequence` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/render-sequence.md
- `reset_niagara_system` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/reset-niagara-system.md
- `run_all_automation_tests` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-all-automation-tests.md
- `run_automation_test` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-automation-test.md
- `run_automation_tests_by_category` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-automation-tests-by-category.md
- `run_editor_utility_blueprint` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-editor-utility-blueprint.md
- `run_editor_utility_widget` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-editor-utility-widget.md
- `run_gauntlet` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-gauntlet.md
- `run_map_check` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-map-check.md
- `run_stat_command` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/run-stat-command.md
- `spawn_niagara_at_location` — Execute — https://policylayer.com/tools/jjpxdev-unreal-mcp/spawn-niagara-at-location.md
- …and 96 more: https://policylayer.com/tools/jjpxdev-unreal-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=jjpxdev-unreal-mcp · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/jjpxdev-unreal-mcp