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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, covering safety and idempotency. The description adds the insight that it returns aggregated period-specific data, but does not elaborate on potential limitations (e.g., date range definition, pagination, or performance). The additional context is modest but does not contradict 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?

The description consists of two short sentences: the first states the tool's output, and the second provides a usage context. Every word is necessary; there is no repetition or fluff. It is well-structured and front-loaded with the most critical information.

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?

Given the lack of parameters, the presence of an output schema (which documents return format), and clear annotations, the description adequately covers the tool's functionality. However, it does not define what 'this period' means (e.g., current month, fiscal year) or whether the data is real-time or cached. This minor gap prevents a perfect score.

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 input schema has zero parameters, and schema description coverage is 100%, meaning there are no parameter semantics to clarify. The description's mention of 'this period' implies a time context, but since no date parameters exist, this does not require further documentation. A higher score is not warranted because the description adds no parameter details beyond the schema.

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 specifies the exact resource ('invoice stats') and lists concrete metrics ('Outstanding totals, overdue counts, and revenue this period'). This clearly distinguishes it from sibling tools like 'get_booking_stats' or 'get_dashboard_stats', which target different data. The verb 'get' combined with the specific metric names makes the purpose unambiguous.

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 mentions 'Used by the weekly-snapshot playbook,' which hints at an automated context but does not explicitly state when to use this tool versus alternatives like 'get_invoice' (single invoice) or 'list_invoices'. No guidance is given on scenarios that would make this tool more appropriate than similar stat tools, leaving the agent to infer usage boundaries.

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