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

Annotations only declare destructiveHint=true, so the description carries the rest of the load. It usefully adds that the list is empty on creation, that it's a write operation, and that it returns the new ID, but it says nothing about duplicate-name behavior, permission requirements, or irreversibility. No contradiction with the annotations.

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?

Three terse fragments with the mutation nature and outcome front-loaded; zero wasted words.

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 statement that it returns the new list's ID fills an important gap, and all four parameters are fully documented by the schema. A note on duplicate names or permissions would round it out, but it is nearly complete for this tool's complexity.

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 the schema already documents name, preferences, and the two URL fields. The description adds no parameter-level detail beyond that, which is acceptable at full coverage.

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 ('create a new, empty mailing list'), disambiguating it from the read-side siblings like moosend_get_mailing_list and moosend_list_mailing_lists. The 'empty' qualifier and the endpoint notation make the scope unambiguous.

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 'WRITE:' prefix signals a mutation and 'create a new' implies the novelty condition, but there is no explicit when-to-use vs. when-not guidance and no alternatives named (e.g., how this differs from adding subscribers or updating an existing list).

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