choose_foundry_instance

Server FoundryMCP thestranjer/foundry-vtt-mcp

Category Write

Risk class Medium

Parameters 00 required

WHAT IT DOES

What choose_foundry_instance does on FoundryMCP

AI agents use choose_foundry_instance to create or update resources in FoundryMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your FoundryMCP environment.

WHY IT NEEDS A POLICY

Why choose_foundry_instance needs a policy

An AI agent can call choose_foundry_instance faster than any human can review — one bad instruction and it creates or modifies resources in FoundryMCP by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

choose_foundry_instance Rate-limited

choose_foundry_instance 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "choose_foundry_instance": {
      "limits": [
        {
          "counter": "choose_foundry_instance_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches FoundryMCP, so you can run agents against it safely.

FAQ

Questions about choose_foundry_instance

What does the choose_foundry_instance tool do? +

Switch to a different Foundry instance. Disconnects from the current instance (if any) and connects to the specified one. You can identify the instance either by item_order (zero-based index) or by _id (the name of the credential entry). Use show_credentials first to see available instances. It is categorised as a Write tool in the FoundryMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on choose_foundry_instance? +

Register the Foundry MCP server in PolicyLayer and add a rule for choose_foundry_instance: 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 FoundryMCP. Nothing to install.

What risk level is choose_foundry_instance? +

choose_foundry_instance is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit choose_foundry_instance? +

Yes. Add a rate_limit block to the choose_foundry_instance 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.

How do I block choose_foundry_instance completely? +

Set action: deny in the PolicyLayer policy for choose_foundry_instance. 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.

What MCP server provides choose_foundry_instance? +

choose_foundry_instance is provided by the Foundry MCP server (thestranjer/foundry-vtt-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.