Get subscriber counts

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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description usefully clarifies that this returns an aggregate (total plus free/paid breakdown) rather than a subscriber list, but says nothing about freshness/staleness or how the default publication is resolved beyond the schema.

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 short sentences, front-loaded with the return content before the routing hint, with no filler. Every sentence earns its place.

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 zero-required-param read tool whose annotations already carry the safety profile, the description tells the agent what it gets back (total, free vs paid). With no output schema, slightly more detail on the return shape or freshness would make it fully self-sufficient.

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 coverage is 100% for the single optional 'publication' parameter, including loose hostname matching and the default-to-first-publication behavior, so the description adds no additional parameter meaning. Baseline 3 applies.

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?

States the resource and exactly what is returned: total subscribers split by free/paid, which is a count aggregation rather than a listing. It does not name the sibling it replaces (list_subscribers, export_subscribers) or otherwise differentiate itself explicitly from them, so it falls just short of 5.

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?

The phrase "fastest way to answer 'how many subscribers do I have'" implies this tool should be preferred over the subscriber-listing siblings for count questions, which is genuine but indirect guidance. There is no explicit when-not condition and no sibling is named, so usage must be inferred.

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