instantiate_prefab
Spawn a prefab instance into the active scene at an optional position and rotation
This record as markdown: /tools/sbox/instantiate-prefab.md
What instantiate_prefab does on Sbox
AI agents use instantiate_prefab to create or update resources in Sbox, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Sbox environment.
Why instantiate_prefab is rated Medium
The tool creates a new object in the scene by spawning a prefab instance. This is a reversible write/create operation — the spawned object can be removed — so it falls under Write rather than Execute or Destructive. Misuse could clutter or corrupt scene state but is generally recoverable.
From the tool's definition Spawn a prefab instance into the active scene at an optional position and rotation
Attacks that exploit this kind of access
The rule that runs instantiate_prefab safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Sbox, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For instantiate_prefab, this is the rule to start with:
instantiate_prefab 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 Sbox, apply this rule, and every instantiate_prefab call is checked against it from then on.
Questions about instantiate_prefab
Spawn a prefab instance into the active scene at an optional position and rotation. It is categorised as a Write tool in the Sbox MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Sbox MCP server in PolicyLayer and add a rule for instantiate_prefab: 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 Sbox. Nothing to install.
instantiate_prefab 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 instantiate_prefab 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 instantiate_prefab. 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.
instantiate_prefab is provided by the Sbox MCP server (sbox-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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