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

Annotations already cover the safety profile (readOnly, idempotent, non-open-world), so the description's job is added context, and it delivers: prices are the real checkout price with fees, marketplaces are opt-in, and the return is a one-sentence decision plus a Fairly link that is omitted when a subscription wins, with subscription_code identifying the winner. It does not mention latency, rate limits, or failure modes when a game is not found in any store.

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?

It is front-loaded with the routing signals (the example questions), then the comparison behavior, then the alternative-tool rule. No sentence is redundant given the payload of behavioral detail each carries.

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?

There is no output schema, and the description compensates by explaining the return shape: a one-sentence decision, a Fairly link for store winners, no link for subscription winners, and subscription_code to identify the subscription. Combined with the 100%-covered input schema, an agent has everything needed to call and interpret it.

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 (region, game_id, currency, include_marketplaces) are already documented with formats, defaults, and examples in the schema. The description only lightly reinforces include_marketplaces ('optionally key marketplaces'); baseline 3 is warranted when the schema does the heavy lifting.

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 names a concrete decision task (cheapest way to play a given game) and what it compares: authorized stores, optionally key marketplaces, and subscriptions at real checkout price with fees. It explicitly contrasts itself with the sibling get_offers, so an agent can route without opening either schema.

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?

It gives three literal example questions that map to when to call it, and states the exclusion rule directly: 'Prefer this over get_offers unless the user wants the full price table.' That is explicit when/when-not with a named alternative.

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