send_webhook_message · Discord MCP: Risk & Policy

WHAT IT DOES

What send_webhook_message does on Discord

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

WHY IT NEEDS A POLICY

Why send_webhook_message needs a policy

This tool creates/posts new data (messages) to Discord, which is reversible (messages can be deleted). It does not execute code, delete data irreversibly, or move money. The 'medium' severity reflects that an AI agent could spam messages, impersonate users via custom usernames/avatars, or post harmful content to Discord servers, but the effects are not irreversible and limited to message creation.

From the tool's definition Tool name 'send_webhook_message' and description state it sends messages through Discord webhooks with custom username/avatar customization. This creates new message data in Discord.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_webhook_message Rate-limited

send_webhook_message 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": {
    "send_webhook_message": {
      "limits": [
        {
          "counter": "send_webhook_message_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 Discord, so you can run agents against it safely.

FAQ

Questions about send_webhook_message

What does the send_webhook_message tool do? +

Send a message through a Discord webhook. Supports custom username and avatar. It is categorised as a Write tool in the Discord 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_webhook_message? +

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

What risk level is send_webhook_message? +

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

Can I rate-limit send_webhook_message? +

Yes. Add a rate_limit block to the send_webhook_message 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_webhook_message completely? +

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

send_webhook_message is provided by the Discord MCP server (ngoctranfire/discord-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.