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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuine value beyond them by flagging that rating breakdowns and comparable items are returned only "when exposed," warning the agent that these subfields can be absent instead of always present.

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?

Two sentences, each earning its place: the first describes the payload, the second routes to alternatives. The scope and the sibling pointer are front-loaded rather than buried, with no filler.

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?

An output schema exists, so return values need not be explained, and annotations carry the safety profile. The description covers purpose, payload, and routing, leaving only an explicit "when to call this" trigger implicit for what is a simple single-URL lookup 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?

With one parameter and 100% schema coverage, the schema already defines the url field and its exact provenance. The description adds no format, validation, or constraint detail beyond that, so the baseline of 3 is appropriate when structured data does the heavy lifting.

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 ("Fetch") and resource ("Fanatics product details and available sizes"), then enumerates the concrete payload contents. It explicitly names the sibling tools that find products, so an agent can separate this detail-lookup tool from the search/category tools without opening any schema.

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?

"Use fanatics_search or fanatics_category to find products" routes the agent to the correct alternatives and implies this tool is used once a product URL is already known. It gives clear context but never states the positive trigger ("use this when you already have a product-detail URL") as an explicit rule.

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