modify_message · Gmail MCP Server MCP: Risk & Policy

WHAT IT DOES

What modify_message does on Gmail MCP Server

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

WHY IT NEEDS A POLICY

Why modify_message needs a policy

Modifying message labels is a non-destructive change to email metadata. While this can affect message visibility and organization (e.g., moving to spam or archive via labels), the operation is reversible—labels can be re-applied or removed. This is less severe than Destructive (which would be permanent deletion) and more impactful than Read.

From the tool's definition Tool description states it 'Modify the labels on a message' — a reversible modification operation. The verb 'modify' combined with the action of changing labels (adding/removing) fits the Write category: creates or modifies data reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

modify_message Rate-limited

modify_message 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": {
    "modify_message": {
      "limits": [
        {
          "counter": "modify_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about modify_message

What does the modify_message tool do? +

Modify the labels on a message. It is categorised as a Write tool in the Gmail 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 modify_message? +

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

What risk level is modify_message? +

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

Can I rate-limit modify_message? +

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

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

modify_message is provided by the Gmail MCP Server MCP server (nk900600/gmail-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.