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

Annotations already declare the operation read-only, idempotent, non-destructive, and closed-world, so the safety profile is covered structurally. The description adds that contact counts accompany each list, which is useful output context beyond the annotations, but it does not discuss ordering, pagination, or return shape.

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?

The description is a single front-loaded sentence with no filler. It communicates the essential behavior directly.

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 zero-parameter, read-only list tool whose annotations fully cover the safety profile, the description is largely complete: it says what is listed and that counts are included. It could be slightly richer about whether all lists are returned, but no output schema exists and no parameters are present to document.

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?

The tool has zero parameters, so there is no parameter semantics to compensate for. The baseline score for zero parameters 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?

The description states a specific verb and resource: listing contact lists, and adds that contact counts are included. This clearly distinguishes it from single-list retrieval such as get_list and from contact-within-list operations such as list_list_contacts, though it does not name those siblings explicitly.

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 the zero-parameter read-only nature: call it when you need to enumerate contact lists. However, the description gives no explicit when-to-use condition, no exclusions, and no routing guidance relative to get_list or list_list_contacts.

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