mention_users · Slack MCP Server MCP: Risk & Policy

WHAT IT DOES

What mention_users does on Slack MCP Server

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

WHY IT NEEDS A POLICY

Why mention_users needs a policy

The tool creates/posts messages to Slack, which is a Write category action. Severity is medium because while message creation is reversible and has limited blast radius, it could be misused to send misleading or harassing messages to multiple users at scale. It does not delete data (not Destructive), execute arbitrary code (not Execute), or involve financial transactions (not Financial).

From the tool's definition Tool sends messages mentioning specific users ('Enviar mensagem mencionando usuários específicos' - send message mentioning specific users). This is a write operation that creates new data (messages) in Slack, which is reversible (messages can be deleted).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

mention_users Rate-limited

mention_users 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": {
    "mention_users": {
      "limits": [
        {
          "counter": "mention_users_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 Slack MCP Server, so you can run agents against it safely.

FAQ

Questions about mention_users

What does the mention_users tool do? +

Enviar mensagem mencionando usuários específicos. It is categorised as a Write tool in the Slack MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on mention_users? +

Register the Slack MCP Server MCP server in PolicyLayer and add a rule for mention_users: 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 Slack MCP Server. Nothing to install.

What risk level is mention_users? +

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

Can I rate-limit mention_users? +

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

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

mention_users is provided by the Slack MCP Server MCP server (will2023a/mcp-slack). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.