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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description usefully adds result shape (max 5 matches, fair value in EUR, product-page url) and the closed-catalog limits, which is genuine value beyond annotations. It still omits what happens on zero results and whether 'fair value' is a single price or a range.

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 tight sentences, front-loaded with what the tool does, followed by return shape and then limits. Every clause carries information and nothing is repeated from the annotations.

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 correctly takes on the return contract (match count, EUR fair value, url). Its remaining gap is the two undocumented optional parameters, which is significant for a 3-parameter tool but does not block a basic call since 'q' alone is required and documented.

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%: 'q' is documented, but 'game' and 'language' have no descriptions and no enums, so the agent must guess their accepted values and defaults. The description never mentions these parameters; the 'Japanese/Korean/Chinese' sentence only hints that language matters, without explaining how to set it.

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 ('Look up') and a tightly scoped resource ('sealed product (ETB, display, tin, UPC…) by name'), which distinguishes it from the sibling lookup_card by scope rather than by explicit mention. An agent can infer this is the sealed-product lookup without opening the schema, though the card/sealed split is never said outright.

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?

Provides two real exclusions: 'Never marketplace listings' and no sealed catalog for Japanese/Korean/Chinese binders. It stops short of naming alternatives (lookup_card for singles, list_sealed for the collection) or saying what to do when a language has no catalog, so routing still requires inference.

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