AI agents use vrchat_join_group to create or update resources in VRChat MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your VRChat MCP Server environment.
Joining a group is a reversible write action (membership can be cancelled/left), creating a new relationship record. It does not delete data, execute code, or involve finances. Misuse could cause the AI to join unintended or inappropriate groups on behalf of the user, hence medium severity.
From the tool's definition 'Join a VRChat group by ID' — creates a membership/association between the user and the group
Documented attack patterns abuse exactly the kind of access vrchat_join_group gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and VRChat MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for vrchat_join_group:
{
"version": "1",
"default": "deny",
"tools": {
"vrchat_join_group": {
"limits": [
{
"counter": "vrchat_join_group_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}vrchat_join_group 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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Join a VRChat group by ID. It is categorised as a Write tool in the VRChat MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the VRChat MCP Server MCP server in PolicyLayer and add a rule for vrchat_join_group: 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 Server. Nothing to install.
vrchat_join_group 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 vrchat_join_group 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 vrchat_join_group. 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.
vrchat_join_group is provided by the VRChat MCP Server MCP server (sawa-zen/vrchat-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 5 VRChat MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
5 VRChat MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.