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

The description adds valuable behavioral context beyond the annotations (readOnly, idempotent, non-destructive). It specifies that counts include only certified publishable dependencies and that uncertified families report zero instead of falling back to legacy data. It also discloses the free nature ('FREE — no payment required') and explicitly lists the return shape. These traits are not present in the annotations and significantly aid the agent in understanding side effects and interpretation.

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 concise yet comprehensive. It front-loads the core purpose, then provides usage guidance, a critical behavioral caveat, return structure, and related tools. Each sentence earns its place; there is no fluff or redundancy. The structure flows logically from purpose to usage to details.

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 that the tool has no parameters and no output schema, the description compensates fully. It specifies the exact fields returned, the source and semantics of counts, when to use it, and related alternatives. This is complete enough for an agent to invoke and interpret the results without further documentation.

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 the schema coverage is effectively 100% and there is no parameter semantics to add. The description does not need to explain any parameters. Per the rubric, the baseline for 0 params is 4. No deductions are warranted; the description appropriately omits parameter detail.

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 opens with a specific verb+resource: 'Get current counts from ShippingRates customer-published datasets.' It clearly defines the tool's scope and differentiates it from siblings by naming alternatives in the final sentence: 'Use shippingrates_lines for per-carrier breakdowns, shippingrates_search for keyword discovery.' This makes the purpose unambiguous and distinct from related tools.

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?

Explicit usage direction is provided: 'Use this before calling data tools.' This tells the agent when to invoke this tool in a workflow. Additionally, it states alternatives for specific needs, e.g., 'shippingrates_lines for per-carrier breakdowns, shippingrates_search for keyword discovery.' This fully addresses when-to-use vs alternatives.

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