rejoin_group · Groupme MCP: Risk & Policy

WHAT IT DOES

What rejoin_group does on Groupme

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

WHY IT NEEDS A POLICY

Why rejoin_group needs a policy

This tool modifies membership state by adding the user back to a group they had left. It is a reversible write operation (membership can be left again), not destructive or financial. The blast radius is medium since it affects group membership visibility and communication access.

From the tool's definition Rejoin a group you previously left

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

rejoin_group Rate-limited

rejoin_group 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": {
    "rejoin_group": {
      "limits": [
        {
          "counter": "rejoin_group_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 Groupme, so you can run agents against it safely.

FAQ

Questions about rejoin_group

What does the rejoin_group tool do? +

Rejoin a group you previously left. It is categorised as a Write tool in the Groupme MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on rejoin_group? +

Register the Groupme MCP server in PolicyLayer and add a rule for rejoin_group: 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 Groupme. Nothing to install.

What risk level is rejoin_group? +

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

Can I rate-limit rejoin_group? +

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

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

rejoin_group is provided by the Groupme MCP server (kalebjs/groupme-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.