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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is established. The description adds behavior beyond the schema by indicating that the result spans all lists and is paginated, which an agent needs when collecting the full set. No contradiction with 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?

One efficient sentence that puts the action and resource up front and appends the pagination qualifier. No wasted words or repetition of annotations.

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 straightforward read-only list tool, the description plus fully documented parameters and safety annotations cover most of what an agent needs. It lacks explicit response-shape details or default pagination behavior, but these are not critical given the simplicity and absence of an output schema.

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, limit, and api_key each have meaningful descriptions. The description adds little beyond reinforcing pagination, so a baseline score of 3 is appropriate because the schema does the heavy lifting.

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?

The description uses a specific verb ('List') and resource ('MailerCloud contact lists') and states the scope ('all') plus pagination. This clearly differentiates it from siblings like get_list_details, create_list, and list_contacts.

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 description implies use when the agent needs to enumerate contact lists rather than inspect a single list, create, update, or delete one. It does not explicitly state when not to use it or name alternative tools, so guidance is only implied, not explicit.

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