join_chat_by_link · Tg MCP: Risk & Policy

WHAT IT DOES

What join_chat_by_link does on Tgmcp

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

WHY IT NEEDS A POLICY

Why join_chat_by_link needs a policy

Joining a chat is a reversible write action — it modifies the account's chat membership state by adding it to a new group/channel. It does not delete data, execute code, or move money. It can be misused to silently join the agent's account to arbitrary chats, hence medium severity.

From the tool's definition Join a chat by invite link

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

join_chat_by_link Rate-limited

join_chat_by_link 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": {
    "join_chat_by_link": {
      "limits": [
        {
          "counter": "join_chat_by_link_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 Tgmcp, so you can run agents against it safely.

FAQ

Questions about join_chat_by_link

What does the join_chat_by_link tool do? +

Join a chat by invite link. It is categorised as a Write tool in the Tgmcp MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on join_chat_by_link? +

Register the Tg MCP server in PolicyLayer and add a rule for join_chat_by_link: 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 Tgmcp. Nothing to install.

What risk level is join_chat_by_link? +

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

Can I rate-limit join_chat_by_link? +

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

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

join_chat_by_link is provided by the Tg MCP server (oevortex/tgmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.