modify_event · Gcal MCP: Risk & Policy

WHAT IT DOES

What modify_event does on Gcal

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

WHY IT NEEDS A POLICY

Why modify_event needs a policy

Modifying calendar events is a reversible write operation—changes can be undone or corrected. It does not delete data permanently (Destructive), execute arbitrary code (Execute), involve financial transactions (Financial), or merely read data (Read).

From the tool's definition Tool name 'modify_event' combined with server description stating it 'manage events' and 'creating, and modifying calendar entries'. The description field is empty, but the name and context clearly indicate modification of existing calendar events.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

modify_event Rate-limited

modify_event 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_event": {
      "limits": [
        {
          "counter": "modify_event_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 Gcal, so you can run agents against it safely.

FAQ

Questions about modify_event

What does the modify_event tool do? +

modify_event. It is categorised as a Write tool in the Gcal 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_event? +

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

What risk level is modify_event? +

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

Can I rate-limit modify_event? +

Yes. Add a rate_limit block to the modify_event 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_event completely? +

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

modify_event is provided by the Gcal MCP server (jdcc/gcal-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.