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

With readOnlyHint=true already declaring the safety profile, the description adds real value: it documents the returned shape (ID, name, custom fields, tags, preferences) and decodes the SubscribeType status values (1 subscribed, 2 unsubscribed, 3 bounced, 4 removed), which appear nowhere in the schema or annotations. It does not cover not-found/error behavior, keeping it short of a 5.

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?

One front-loaded sentence that leads with the action and key dimensions before listing return fields. It is dense but everything earns its place except the raw REST path, which is arguably redundant for an agent.

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?

No output schema exists, so the description correctly compensates by enumerating returned fields and decoding the status enum. It is nearly complete for a simple lookup, missing only error/empty-result behavior.

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 (email format, list ID as GUID sourced from moosend_list_mailing_lists). The description adds nothing about parameter format or constraints beyond the schema, so the 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 a specific verb and resource ('look up a subscriber'), constrains scope ('in one mailing list by email address'), and enumerates what comes back. The 'by email address' key implicitly distinguishes it from the sibling moosend_get_subscriber (keyed by ID) and moosend_list_subscribers.

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 'look up a subscriber in one mailing list by email address', and the schema notes the list ID comes from moosend_list_mailing_lists. However, there is no explicit when-to-use-vs-alternative guidance (e.g. use moosend_get_subscriber when you have the subscriber ID, or list_subscribers for broad retrieval).

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