Create a prefab variant from an existing base prefab. Variants inherit from the base and can override specific properties.
AI agents use unity_prefab_create_variant 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.
The tool creates new prefab variants by modifying existing assets, which is a reversible write operation. While prefab variants can have project-wide impact through their inheritance relationships (affecting multiple scenes if used), the action itself is not destructive—variants can be deleted and the base prefab remains intact.
From the tool's definition Tool name explicitly states 'create' and description confirms it 'Create[s] a prefab variant from an existing base prefab.' This is a creation operation that modifies project state by adding new variant assets to the project.
Documented attack patterns abuse exactly the kind of access unity_prefab_create_variant 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_create_variant:
{
"version": "1",
"default": "deny",
"tools": {
"unity_prefab_create_variant": {
"limits": [
{
"counter": "unity_prefab_create_variant_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}unity_prefab_create_variant 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.
Create a prefab variant from an existing base prefab. Variants inherit from the base and can override specific properties. 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_create_variant: 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_create_variant 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_create_variant 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_create_variant. 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_create_variant 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.