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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description adds value by detailing the output includes 30/90-day change and price. However, it doesn't disclose default behavior (scope defaults to 'all', limit defaults to 10) or that source can be tcgplayer or cardtrader. The mention of 'Cardmarket's price' alone could mislead agents into assuming only one source is available, which contradicts the schema's enum.

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?

A single, well-structured sentence that front-loads the core purpose ('most valuable Gundam cards') and then adds details on scoping and output. No redundancy or fluff.

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 simple listing tool with four parameters and no output schema, the description covers the core function but misses default parameter values and the full set of price sources. The single mention of 'Cardmarket's price' is incomplete given the schema allows tcgplayer and cardtrader. Overall adequate but with notable gaps.

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 covers slug and source with descriptions; the description clarifies that slug can be a set code or rarity slug, and explains the sorting. Limit and scope are not elaborated beyond the schema's enums, but the phrase 'in one set or rarity tier' hints at scope usage. Partial value is added, but the description doesn't fully compensate for the 50% schema coverage.

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 clearly states that the tool returns the most valuable Gundam cards, sorted by price descending, with 30/90-day change and price info. It specifies the resource (cards) and the key output fields. It doesn't explicitly differentiate from siblings like market_movers or best_buys, but the 'most valuable' focus gives a distinct purpose.

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?

There is no explicit guidance on when to use this tool versus alternatives like market_movers or best_buys. It implies usage for valuation queries but doesn't state exclusions, conditions, or when to prefer another tool. The description only provides context on scope (set/rarity) without routing to alternatives.

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