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

Annotations already declare readOnlyHint=true, and the description adds meaningful context beyond that: the exact endpoint and pagination structure (GET /lists/{Page}/{PageSize}.json), plus the specific return payload fields. It does not address rate limits or default sort behavior, which keeps it below 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?

Front-loaded with the payload scope, then a short rationale, then the endpoint. Three compact sentences with little waste, though the parenthetical field enumeration makes the first sentence slightly dense.

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 no output schema, the description compensates by naming the returned fields (member counts, custom fields, preferences, paging), so an agent knows what to expect. Combined with readOnlyHint and a fully documented input schema, the definition is nearly self-sufficient; only default-ordering behavior is left implicit.

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% (page, page_size, sort_by, sort_method all documented with defaults and ranges), so the schema carries parameter meaning. The description only adds 'paging info' generically and the endpoint path showing {Page}/{PageSize}, providing no syntax or format detail beyond the schema. 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 ('List the active email (mailing) lists in the account') and enumerates the returned content: member counts, custom field definitions, preferences, and paging info. This clearly separates it from siblings like moosend_get_mailing_list and moosend_create_mailing_list.

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?

Gives a concrete usage context — 'a cheap way to confirm the API key works and to find list IDs' — which is actionable discovery guidance. It stops short of naming alternatives or exclusion conditions (e.g., when to prefer get_mailing_list for full detail), so it is clear but not fully routing.

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