mark_read · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What mark_read does on Nexus Core

AI agents use mark_read 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 mark_read needs a policy

This is a Write operation because it modifies message attributes (label removal) rather than just reading data. The change is reversible—labels can be re-applied—so it is not Destructive. The severity is low because marking messages as read has minimal blast radius; it affects only message metadata visibility and does not expose sensitive data, delete content, or trigger external actions.

From the tool's definition Tool description states it removes the UNREAD label from messages, which modifies message state. The verb 'remove' indicates a reversible alteration of metadata.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

mark_read Rate-limited

mark_read 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": {
    "mark_read": {
      "limits": [
        {
          "counter": "mark_read_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 mark_read

What does the mark_read tool do? +

Remove the UNREAD label from one or more messages. 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 mark_read? +

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

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

Can I rate-limit mark_read? +

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

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

mark_read 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.