add_label · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What add_label does on Nexus Core

AI agents use add_label 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 add_label needs a policy

This tool modifies Gmail state by creating labels and tagging messages, which are reversible operations. It does not execute code, delete data irreversibly, or move financial resources. The severity is medium because label manipulation could be misused to hide/organize sensitive messages or spam, affecting email organization and visibility, but labels can be removed and do not cause data loss.

From the tool's definition "Apply a Gmail label to a message. Creates the label if it doesn't exist." — the tool creates new labels (reversibly) and modifies message metadata by applying labels.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_label Rate-limited

add_label 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": {
    "add_label": {
      "limits": [
        {
          "counter": "add_label_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 add_label

What does the add_label tool do? +

Apply a Gmail label to a message. Creates the label if it doesn't exist. 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 add_label? +

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

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

Can I rate-limit add_label? +

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

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

add_label 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.