unity_prefab_set_reference
Wire an ObjectReference property on a component inside a prefab asset — no scene instance needed. Can reference project assets (materials, textures, prefabs, ScriptableObjects) or other GameObjects within the same prefab.
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What unity_prefab_set_reference does on Unity MCP Server
AI agents use unity_prefab_set_reference to create or update resources in Unity MCP Server, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Unity MCP Server environment.
Why unity_prefab_set_reference is rated Medium
This tool modifies prefab asset data by setting ObjectReference properties on components. While this is destructive-adjacent (prefabs are project assets), the operation is reversible—references can be changed or cleared without permanent data loss. It falls under Write rather than Destructive because the prefab asset itself is not deleted and the change can be undone.
From the tool's definition Tool name 'unity_prefab_set_reference' and description 'Wire an ObjectReference property on a component inside a prefab asset' indicate modification of prefab component properties.
Attacks that exploit this kind of access
The rule that runs unity_prefab_set_reference safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Unity MCP Server, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For unity_prefab_set_reference, this is the rule to start with:
unity_prefab_set_reference stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Unity MCP Server, apply this rule, and every unity_prefab_set_reference call is checked against it from then on.
Questions about unity_prefab_set_reference
Wire an ObjectReference property on a component inside a prefab asset — no scene instance needed. Can reference project assets (materials, textures, prefabs, ScriptableObjects) or other GameObjects within the same prefab. It is categorised as a Write tool in the Unity MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Unity MCP Server MCP server in PolicyLayer and add a rule for unity_prefab_set_reference: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Unity MCP Server. Nothing to install.
unity_prefab_set_reference is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the unity_prefab_set_reference rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for unity_prefab_set_reference. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
unity_prefab_set_reference is provided by the Unity MCP Server MCP server (anklebreaker-studio/unity-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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