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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add context — and it does: it discloses the HobbyCardIndex API-key requirement and that the payload includes a link to recent sales and price history. No return-shape detail beyond that, which is acceptable given an output schema exists.

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 dense, front-loaded sentences: the payload description comes first, the provenance/auth constraints second. No filler, no restated tool name, every clause carries information an agent needs.

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?

For a one-parameter read tool with an output schema and full annotation coverage, the description covers the remaining gaps — what the grades are, the currency, the return link, and the auth requirement. Nothing needed to call it correctly is missing.

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 description coverage is 100% and the single card_id parameter is already documented as coming from search_cards, so the description's reference to that same origin adds little beyond the structured field. Baseline 3 is appropriate for a fully documented parameter.

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 and resource — current sold prices for one card, enumerated by grade — plus currency (USD) and the exact grade breakdown. An agent can tell instantly that this is a per-card price lookup, distinct from the sibling search_cards which only locates cards.

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?

Explicitly names search_cards as the source for card_id, establishing the search-then-price workflow, and states the API-key prerequisite. It lacks an explicit 'do not call with X' exclusion, but the sequencing guidance is clear enough to act on.

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