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

Annotations already declare a safe, idempotent, closed-world read, so the bar is lower; the description still adds real value by disclosing the plan gating and the exact shape of the free-plan error ('readable error naming the upgrade needed'). It also states the per-variant grouping guarantee, though it doesn't discuss empty-result behavior or whether short windows return partial aggregates.

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?

Front-loads the verb, resource, and scope, then enumerates outputs compactly in a single dense sentence. The paid-plan sentence is short and earns its place; nothing is padded, though the output-field enumeration runs long given an output schema exists.

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 a full input schema, an output schema covering return values, and read-only annotations, the description fills the remaining gaps an agent needs: the plan gate, error behavior, and the guarantee that variants are never blended. Nothing required 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%, so all four parameters are already documented, and the enum values for window and response_format are visible there. The description only reinforces the window choices and the per-variant semantics of 'variant'; it says nothing extra about response_format or the id format from binderdex_search_cards, so baseline 3 applies.

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 (aggregate price statistics for one card) and precisely enumerates the returned metrics: min, max, average, first/last price with dates, and percent change. The 'per variant so printings are never blended together' clause distinguishes it from the raw history sibling at binderdex_get_price_history.

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 clear context for use: one card, a 7/30/90-day window, and a paid-plan prerequisite with a described failure mode for free keys. It does not, however, explicitly route the agent between this tool and binderdex_get_price_history or binderdex_value_cards, so the alternative-selection guidance is only implicit.

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