expression_set · Live2d To Agent MCP: Risk & Policy

WHAT IT DOES

What expression_set does on Live2d To Agent

AI agents invoke expression_set to trigger actions in Live2d To Agent. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why expression_set needs a policy

This tool triggers an external operation on the Live2D desktop pet application — changing the character's displayed expression. It is not a pure read, and it modifies the state of an external application in real-time. The blast radius is low since it only affects a cosmetic desktop animation with no data loss or financial impact.

From the tool's definition 切换 Live2D 角色的表情。根据对话情绪选择合适的表情。 (Switch Live2D character expression; select appropriate expression based on conversation emotion)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

expression_set Rate-limited

expression_set stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "expression_set": {
      "limits": [
        {
          "counter": "expression_set_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Live2d To Agent, so you can run agents against it safely.

FAQ

Questions about expression_set

What does the expression_set tool do? +

切换 Live2D 角色的表情。根据对话情绪选择合适的表情。. It is categorised as a Execute tool in the Live2d To Agent MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on expression_set? +

Register the Live2d To Agent MCP server in PolicyLayer and add a rule for expression_set: 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 Live2d To Agent. Nothing to install.

What risk level is expression_set? +

expression_set is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit expression_set? +

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

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

expression_set is provided by the Live2d To Agent MCP server (lmy414/live2d-to-agent). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.