AI agents use set_avatar_parameter to create or update resources in VRChat MCP OSC — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your VRChat MCP OSC environment.
This tool modifies avatar state by setting a parameter value. It creates or changes data (avatar parameters) in a reversible way — parameters can be changed again. No code execution, deletion, or financial impact is involved. Misuse could cause unintended avatar behavior in VRChat, giving it a medium severity.
From the tool's definition Set a parameter on the current avatar
Documented attack patterns abuse exactly the kind of access set_avatar_parameter gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and VRChat MCP OSC, and nothing reaches the server without passing your rules. This is the rule we recommend for set_avatar_parameter:
{
"version": "1",
"default": "deny",
"tools": {
"set_avatar_parameter": {
"limits": [
{
"counter": "set_avatar_parameter_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_avatar_parameter 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.
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Set a parameter on the current avatar. It is categorised as a Write tool in the VRChat MCP OSC MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the VRChat MCP OSC MCP server in PolicyLayer and add a rule for set_avatar_parameter: 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 VRChat MCP OSC. Nothing to install.
set_avatar_parameter 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 set_avatar_parameter 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 set_avatar_parameter. 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.
set_avatar_parameter is provided by the VRChat MCP OSC MCP server (krekun/vrchat-mcp-osc). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from VRChat MCP OSC, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
12 VRChat MCP OSC tools catalogued and risk-classified — across an index of 43,000+ MCP servers.