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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds genuinely useful non-schema context: the 3-credit cost and the implicit 10 EUR minimum card value, which affect whether an agent should call it. It does not describe the response shape or ordering, but with annotations carrying safety this lands at a 3.

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 compact sentences, front-loaded with what the tool returns and immediately followed by the credit cost. No filler and nothing an agent must read twice.

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 7-parameter, no-output-schema tool the description is nearly sufficient: scope, time windows, price floor and cost are all stated. It omits what a result entry looks like (card identity, price change, percentage) and how the `reliable` flag and `direction` combine in practice, but the rich schema descriptions compensate for most of that.

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 86%, so the schema already explains game, period, language, reliable, direction and edition_id in detail. The description restates the period options and adds the 10 EUR threshold, which is a real filter not expressed in the schema, but it offers no additional meaning for limit, language or edition_id. Baseline 3 is appropriate.

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 gives a specific verb and resource: 'largest price rises or falls of a game or an edition' with the time windows and a price floor. An agent can distinguish it conceptually from siblings like top_priced (most expensive) and get_price_history (per-card history), though neither sibling is named explicitly.

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?

Usage is implied by the framing (movers over 7/30/90 days for cards >= 10 EUR), which tells the agent the shape of question this answers. However, there is no explicit when-to-use guidance, no mention of when to prefer top_priced or get_price_history instead, and no stated prerequisites such as needing a game slug from list_games (that hint lives only in the schema).

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