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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description earns credit for disclosing the valuation source (PokéItem fair value, not live marketplace data) and for warning that matching is strict across print version, language and condition/slab. It does not say what the comparison returns (verdict, delta, percentage) even though no 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 sentences, front-loaded with the core comparison, with the parentheticals carrying real matching rules rather than filler. Minor cost: the parenthetical distinctions arrive before the reader knows they apply to specific parameters.

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 9-parameter tool with low schema coverage and no output schema, the description covers intent, data source and matching strictness but leaves output shape (verdict vs. numeric delta) and half the parameters unexplained. Adequate to call correctly in the common case, incomplete for edge cases like gradeLabel or gradeValue.

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%, so the description must compensate, and it does: the 'édition 1 ≠ unlimited, PSA 10 ≠ NM raw' note explains why version, language, condition and grader must match the exact copy being priced. The remaining undocumented parameters (game, gradeValue, and the enum-less grader/version fields) still receive no format guidance.

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 — compare an asking price in EUR against the PokéItem fair value for the matching print — and explicitly scopes out what it is not ('Does not fetch or return live marketplace listings'), separating it from lookup_card, card_history and portfolio_analysis.

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?

The comparison framing implies the use case (evaluating a seller's asking price before buying), and the exclusion of live listings hints that listing data must come from elsewhere, but no sibling tool or explicit when-to-use condition is named.

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