send_message_to_user

THE RISK

Medium Risk

Why send_message_to_user needs a policy

Sending a message is a reversible write operation that creates new data (the message itself) in Lark. It modifies the message history and notification state for the recipient but does not delete data or execute arbitrary code. Severity is medium because misuse could spam users or send inappropriate messages, but the impact is containable and does not result in permanent data loss or financial harm.

From the tool's definition Tool description states 'Send a message to the user on Lark' — this creates new message data in the Lark system.

Documented attack patterns abuse exactly the kind of access send_message_to_user gives an agent:

POLICY

How to control send_message_to_user

PolicyLayer is an MCP gateway — it sits between your AI agents and Lark MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_message_to_user:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "send_message_to_user": {
      "limits": [
        {
          "counter": "send_message_to_user_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

send_message_to_user 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.

Create a free account and register Lark MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Lark MCP Server tools

Write add_attendees Add attendees to a calendar event on Lark Write create_event Create a calendar event on Lark Read list_events List events from the user on Lark Read search_user_in_supabase Search for a user in Supabase database by partial name and get their user ID and calendar

All 5 Lark MCP Server tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about send_message_to_user

What does the send_message_to_user tool do? +

Send a message to the user on Lark. It is categorised as a Write tool in the Lark 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 send_message_to_user? +

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

What risk level is send_message_to_user? +

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

Can I rate-limit send_message_to_user? +

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

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

send_message_to_user is provided by the Lark MCP Server MCP server (junyuan-qi/lark-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Lark MCP Server tool call.

Start from Lark MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →