update_tool · Vapi MCP Server MCP: Risk & Policy

WHAT IT DOES

What update_tool does on Vapi MCP Server

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

WHY IT NEEDS A POLICY

Why update_tool needs a policy

This tool creates or modifies data reversibly, fitting the Write category. It updates tool definitions within the Vapi platform, which can be undone by updating again with different values. The severity is medium because misconfiguration of voice AI tools could affect the behavior of automated calls or assistants, but the impact is bounded to this platform and reversible.

From the tool's definition Tool description: 'Updates an existing Vapi tool' — the verb 'Updates' indicates modification of existing data. The tool is part of a voice AI platform's tool management system where tools are likely configurations or definitions used by assistants.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_tool Rate-limited

update_tool 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": {
    "update_tool": {
      "limits": [
        {
          "counter": "update_tool_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 Vapi MCP Server, so you can run agents against it safely.

FAQ

Questions about update_tool

What does the update_tool tool do? +

Updates an existing Vapi tool. It is categorised as a Write tool in the Vapi MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on update_tool? +

Register the Vapi MCP Server MCP server in PolicyLayer and add a rule for update_tool: 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 Vapi MCP Server. Nothing to install.

What risk level is update_tool? +

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

Can I rate-limit update_tool? +

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

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

update_tool is provided by the Vapi MCP Server MCP server (kuchikirenji/mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.