mqtt_publish · MCP MQTT Server MCP: Risk & Policy

WHAT IT DOES

What mqtt_publish does on MCP MQTT Server

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

WHY IT NEEDS A POLICY

Why mqtt_publish needs a policy

Publishing to MQTT topics is a Write operation that sends data outward to potentially many subscribers (IoT devices, actuators, sensors). While reversible in the sense that the message cannot be un-sent, it does not delete data.

From the tool's definition 'Publish a message to an MQTT topic' — creates and sends new messages to an MQTT broker topic

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

mqtt_publish Rate-limited

mqtt_publish 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": {
    "mqtt_publish": {
      "limits": [
        {
          "counter": "mqtt_publish_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 MCP MQTT Server, so you can run agents against it safely.

FAQ

Questions about mqtt_publish

What does the mqtt_publish tool do? +

Publish a message to an MQTT topic. It is categorised as a Write tool in the MCP MQTT 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 mqtt_publish? +

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

What risk level is mqtt_publish? +

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

Can I rate-limit mqtt_publish? +

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

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

mqtt_publish is provided by the MCP MQTT Server MCP server (tspspi/mcpmqtt). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.