check_mqtt
Connect to an MQTT broker and send a CONNECT packet (v3.1.1). Checks for a CONNACK response and decodes the return code. port: 1883 (plain) or 8883 (TLS). Does not authenticate (anonymous connect). Returns whether the broker accepted the connection and its return code.
This record as markdown: /tools/aaronckj-mcp-nettools/check-mqtt.md
What check_mqtt does on Mcp Nettools
AI agents invoke check_mqtt to trigger actions in Mcp Nettools. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why check_mqtt is rated High
This tool actively establishes a network connection to an external MQTT broker and sends protocol packets, triggering external operations. It is not merely reading local data — it performs an outbound connection and interaction with a remote service. This goes beyond Read into Execute territory, as it initiates a session with an external system.
From the tool's definition Connect to an MQTT broker and send a CONNECT packet (v3.1.1). Checks for a CONNACK response
Attacks that exploit this kind of access
The rule that runs check_mqtt safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Mcp Nettools, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For check_mqtt, this is the rule to start with:
check_mqtt stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Mcp Nettools, apply this rule, and every check_mqtt call is checked against it from then on.
Questions about check_mqtt
Connect to an MQTT broker and send a CONNECT packet (v3.1.1). Checks for a CONNACK response and decodes the return code. port: 1883 (plain) or 8883 (TLS). Does not authenticate (anonymous connect). Returns whether the broker accepted the connection and its return code. It is categorised as a Execute tool in the Mcp Nettools MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Mcp Nettools MCP server in PolicyLayer and add a rule for check_mqtt: 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 Nettools. Nothing to install.
check_mqtt is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the check_mqtt 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.
Set action: deny in the PolicyLayer policy for check_mqtt. 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.
check_mqtt is provided by the Mcp Nettools MCP server (aaronckj/mcp-nettools). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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