Set a serialized property value on a component inside a prefab asset — no scene instance needed. Supports floats, ints, strings, bools, vectors, colors, enums.
AI agents use unity_prefab_set_property 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.
This tool creates or modifies data reversibly by changing serialized properties on prefab components. While it alters game assets, the changes are not destructive (can be undone via version control or undo) and do not involve deletion. The high severity reflects the potential blast radius: incorrect property modifications could break game functionality across all instances of a prefab used throughout a project.
From the tool's definition Tool name 'unity_prefab_set_property' and description 'Set a serialized property value on a component inside a prefab asset' directly indicate modification of persistent game asset data.
Documented attack patterns abuse exactly the kind of access unity_prefab_set_property gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Unity MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for unity_prefab_set_property:
{
"version": "1",
"default": "deny",
"tools": {
"unity_prefab_set_property": {
"limits": [
{
"counter": "unity_prefab_set_property_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}unity_prefab_set_property 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.
Free to start. No card required.
Set a serialized property value on a component inside a prefab asset — no scene instance needed. Supports floats, ints, strings, bools, vectors, colors, enums. 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_property: 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_property 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_property 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_property. 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_property 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.
Deterministic rules across all 324 Unity MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
324 Unity MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.