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

Annotations already declare readOnlyHint=true, destructiveHint=false and closed-world scope, so the safety profile is covered. The description adds genuinely useful context beyond that: a $0.05 cost, an API-key requirement, and the meaning of the auto_synced field (marks Family, which follows each contact's relationship).

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?

A single dense sentence that front-loads the verb and resource, then tacks on return fields, a downstream hint, and cost/auth. Efficient and front-loaded, though slightly packed with several concerns.

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?

Covers the operation, the notable auto_synced semantic, cost, auth requirement, and a follow-up tool. An output schema exists so return values need not be explained. Adequate for a simple read-only listing tool.

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?

Only one parameter (include_counts) and schema coverage is 100%, so the schema fully documents it. The description's field list (id, name, slug, member_count, created_at) describes output rather than parameter semantics, so it adds little 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 owner's contact lists') and clarifies the domain ('the lists on Contacts'), plus enumerates returned fields. It also names a related tool (get_people) for the filtering workflow, helping distinguish it from the get_* siblings, though it never explicitly contrasts with create_contact_list or the add/remove list siblings.

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?

'Filter contacts by list with get_people(lists)' gives a downstream workflow hint, implying the output feeds contact filtering. But it never states when to use this tool vs. listing alternatives; usage is implied rather than spelled out.

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