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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the underlying REST route (GET /subscribers/{MailingListID}/find/{SubscriberID}.json), which confirms the read-only, ID-scoped nature, but says nothing about rate limits, 404 behavior, or error handling for a nonexistent subscriber.

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, zero filler, with the tool's purpose front-loaded and the API route as supporting detail. Nothing could be removed without losing information.

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 simple two-parameter read-only getter with full schema coverage and readOnlyHint, the definition covers everything needed to invoke it correctly. The absence of an output schema means return shape is unspecified, but that is a mild gap for a single-record fetch.

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% and both parameters are documented there as GUIDs, including the note that the mailing list ID comes from moosend_list_mailing_lists. The description adds only the route template placement of the two IDs, which the schema effectively already conveys — baseline 3.

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 a specific verb and resource ('Get one subscriber in a mailing list') and pins the lookup key as the subscriber ID, which implicitly distinguishes it from the sibling moosend_get_subscriber_by_email. It doesn't explicitly name that sibling, so it falls short of a 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?

No guidance on when to use this instead of moosend_get_subscriber_by_email, moosend_list_subscribers, or moosend_list_segment_subscribers. The description states what it fetches but leaves the selection decision entirely to inference.

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