update_event · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What update_event does on Nexus Core

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

WHY IT NEEDS A POLICY

Why update_event needs a policy

The tool creates or modifies calendar/event data reversibly. Users can undo or re-modify changes to event properties. This is a classic Write operation—it does not execute arbitrary code, delete irreversibly, or involve financial transactions. Severity is medium because calendar event manipulation could affect scheduling, notifications, and group coordination, but changes are recoverable.

From the tool's definition Tool description states 'Modify event fields' with explicit list of modifiable fields (title, start, end, location, description, attendees), indicating reversible data mutation without deletion.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

update_event Rate-limited

update_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": {
    "update_event": {
      "limits": [
        {
          "counter": "update_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about update_event

What does the update_event tool do? +

Modify event fields. Allowed: title, start, end, location, description, attendees. It is categorised as a Write tool in the Nexus Core 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_event? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for update_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 Nexus Core. Nothing to install.

What risk level is update_event? +

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

Can I rate-limit update_event? +

Yes. Add a rate_limit block to the update_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 update_event completely? +

Set action: deny in the PolicyLayer policy for update_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 update_event? +

update_event is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.