list_subscriptions

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered; the description adds real behavioral context by explaining that results include changes buffered since subscription creation. The notable omission is whether listing drains or leaves the buffer intact, which matters for repeated calls. Strong but not fully complete on mutation-side effects of a read.

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 sentences, both load-bearing: the first defines the payload and its buffered content, the second routes the agent from the subscribe sibling and offers the resource alternative. Nothing is repeated from the name or annotations.

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?

With an output schema present, the description needn't explain return structure, and it correctly focuses on provenance of the data and the alternate access path. The only meaningful gap is buffer-consumption semantics, which an agent calling this repeatedly would want to know.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The description does not need to explain any inputs.

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 gives a specific verb and resource ('List the active OPC UA data-change subscriptions') and adds scope that distinguishes it: each subscription comes with the value changes buffered for it since creation. An agent can tell this apart from subscribe_opcua_nodes, read_opcua_nodes, and list_active_alarms without opening any schema.

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?

It states explicitly when to reach for this tool ('This is how to collect what subscribe_opcua_nodes has been watching') and names an equivalent alternative path (the 'opcua://subscriptions' resource). Both the use condition and the alternate access route are spelled out rather than inferred.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.