Subscribe to an MQTT topic to start receiving messages. Use + and # wildcards for single-level and multi-level topic filters.
Subscribe to an MQTT topic to start receiving messages. Supports MQTT wildcards: '+' for single level, '#' for multi-level.
| Name | Required | Description | Default |
|---|---|---|---|
| qos | No | Quality of Service level (0, 1, or 2). Default is 0. | |
| topic | Yes | The MQTT topic to subscribe to (e.g., 'sensors/temperature' or 'sensors/+/status') |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden, yet it only adds the wildcard syntax rule. It says nothing about subscription persistence, whether re-subscribing to the same topic replaces or duplicates, error behavior for invalid topics, or required broker/auth state.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two tight sentences with the core action front-loaded and the wildcard syntax as supporting detail. Every sentence earns its place with no filler.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a two-parameter tool with a fully documented schema and no output schema, the description covers the essentials, but with zero annotations it omits subscription lifecycle behavior (persistence, duplicate subscriptions, error handling) that an agent would need to call it correctly.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so both parameters are already documented, which sets the baseline at 3. The description adds real meaning for the topic parameter by defining '+' as single-level and '#' as multi-level wildcards, but it says nothing about qos beyond what the schema enum already provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb (subscribe) and resource (MQTT topic) and explains the outcome ('start receiving messages'), so the operation is unambiguous. It does not explicitly differentiate itself from siblings such as mqtt_read_messages or mqtt_list_subscriptions, but the verb alone makes the distinction reasonably clear.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Usage is implied by 'to start receiving messages', which hints at the subscribe-then-receive workflow, but there is no explicit statement of when to subscribe versus use mqtt_read_messages or mqtt_list_subscriptions, nor any prerequisites or exclusions.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.