send_message · Viber MCP: Risk & Policy

WHAT IT DOES

What send_message does on Viber

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

WHY IT NEEDS A POLICY

Why send_message needs a policy

This tool creates and sends individual messages to users, which is a Write operation (creates data/communication). It is reversible and has no destructive capability. Severity is medium because misuse could enable spam or harassment campaigns, but the tool is limited to individual messages (not bulk) and operates within a legitimate messaging platform. Confidence is high as the description is clear and unambiguous.

From the tool's definition Tool name 'send_message' combined with description 'Send a text message to a subscribed Viber user' and 'Returns message_token for delivery tracking' indicates creation/transmission of a message, a reversible communication action.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_message Rate-limited

send_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_message": {
      "limits": [
        {
          "counter": "send_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 Viber, so you can run agents against it safely.

FAQ

Questions about send_message

What does the send_message tool do? +

Send a text message to a subscribed Viber user. Use for plain-text replies or notifications. Do not use for bulk messaging — use broadcast_message instead. Returns message_token for delivery tracking. It is categorised as a Write tool in the Viber 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? +

Register the Viber MCP server in PolicyLayer and add a rule for send_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 Viber. Nothing to install.

What risk level is send_message? +

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

Can I rate-limit send_message? +

Yes. Add a rate_limit block to the send_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_message completely? +

Set action: deny in the PolicyLayer policy for send_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_message? +

send_message is provided by the Viber MCP server (serhiizghama/viber-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.