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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered; the description earns credit for adding context annotations cannot express: field-level exclusions (bank accounts, SSNs, contact details), one-page-per-call pagination, and permission-dependent results. A minor gap is that it does not say what happens when nextToken is exhausted.

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 compact fragments with zero waste, and the most decision-relevant information (what is returned, what is excluded) is front-loaded. The sentence-fragment style is terse but readable.

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 description usefully covers the shape of returned data and the exclusion list, which is the right emphasis. However, for a three-parameter tool it omits any parameter semantics and any usage guidance, leaving real gaps an agent must resolve by inspection.

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 coverage is only 33% – nextToken is documented in the schema, but siteIds (required, 1-100 UUIDs) and includeDeleted have no description anywhere. The description mentions no parameters at all, so it does not compensate for the coverage gap; notably, an agent would not learn from this text that deleted payers can be included.

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 enumerates the returned data (billing identities, names, balances, billing references) which effectively identifies the resource, but it never states a verb such as 'lists bill payers' – the agent must infer the action from the name. It is distinguishable from siblings like famly_list_payments and famly_list_invoices only by implication from the field list.

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?

There is no when-to-use guidance, no statement of when to prefer famly_list_payments or famly_get_invoices instead, and no prerequisites beyond a passing mention that results depend on token permissions. The agent is left to infer all routing decisions.

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