block_focus_time · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What block_focus_time does on Nexus Core

AI agents use block_focus_time 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 block_focus_time needs a policy

The tool creates a new calendar event, which is a Write operation (creates data reversibly). Severity is medium because misuse could flood a calendar with unwanted events, disrupting scheduling, but the action is reversible (events can be deleted). It does not execute arbitrary code, delete data irreversibly, or involve financial transactions.

From the tool's definition Tool description states 'Create a calendar event' — this is a create operation that modifies the calendar reversibly by adding an event.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

block_focus_time Rate-limited

block_focus_time 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": {
    "block_focus_time": {
      "limits": [
        {
          "counter": "block_focus_time_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 block_focus_time

What does the block_focus_time tool do? +

Create a calendar event titled label (default 'Focus') to protect the window. 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 block_focus_time? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for block_focus_time: 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 block_focus_time? +

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

Can I rate-limit block_focus_time? +

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

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

block_focus_time 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.