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

readOnlyHint already covers the safety profile, but the description adds real context beyond it: members are NOT included, results are paginated, and next_page_token should be fed back as page_token. These behavioral traits are not derivable from 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?

Dense but front-loaded: the core purpose comes first, followed by the member-exclusion redirect and pagination mechanics. Minor overlap between the description's account note and the schema's account description.

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 paginated read-only list tool with no output schema, it covers the essentials: scope, member exclusion, pagination token handling, and account selection. Return value structure beyond next_page_token is not described, which is the one small gap.

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 descriptions of limit, account, and page_token are already fully documented in the schema. The description reinforces when to pass account but adds little new semantic detail, so 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 (List) and resource (Google Contacts groups/labels), clarifies the terminology ('what the Google Contacts UI calls labels'), and gives concrete examples including system groups. It distinguishes itself from the sibling get_contact_groups by scoping members out.

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?

Explicitly routes the agent to get_contact_groups with resource_name and max_members when members are needed, and names the condition for passing account (multiple Contacts-enabled accounts). Both the alternative and the when-to-use condition are stated, not implied.

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