skin_apply · Cartridge MCP: Risk & Policy

WHAT IT DOES

What skin_apply does on Cartridge

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

WHY IT NEEDS A POLICY

Why skin_apply needs a policy

This tool modifies the active cartridge's personality configuration, which is a reversible operation consistent with Write category. It does not execute external code or operations, does not delete data, and does not involve financial transactions. The blast radius is limited to the cosmetic/behavioral presentation of the cartridge, with no irreversible side effects.

From the tool's definition Tool name 'skin_apply' and description 'Apply a personality skin to the active cartridge' indicate modification of cartridge state/configuration.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

skin_apply Rate-limited

skin_apply 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": {
    "skin_apply": {
      "limits": [
        {
          "counter": "skin_apply_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 Cartridge, so you can run agents against it safely.

FAQ

Questions about skin_apply

What does the skin_apply tool do? +

Apply a personality skin to the active cartridge. It is categorised as a Write tool in the Cartridge MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on skin_apply? +

Register the Cartridge MCP server in PolicyLayer and add a rule for skin_apply: 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 Cartridge. Nothing to install.

What risk level is skin_apply? +

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

Can I rate-limit skin_apply? +

Yes. Add a rate_limit block to the skin_apply 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 skin_apply completely? +

Set action: deny in the PolicyLayer policy for skin_apply. 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 skin_apply? +

skin_apply is provided by the Cartridge MCP server (lucineer/cartridge-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.