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

Annotations already declare readOnlyHint and openWorldHint, yet the description still adds substantive traits: upstream source (Apple iTunes Lookup API), the rating-count-zero fallback, per-successful-call pricing of $0.002 USDC, accepted payment rails (Base, Solana, Arc), and that failed calls are not charged. That billing and fallback detail is exactly the kind of context annotations cannot convey.

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?

The payload and scope are front-loaded, and the pricing clause earns its place because it affects whether the agent should call at all. It is a single dense sentence plus one billing sentence, with no filler, though it borders on cramped.

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 an output schema present, return-value structure needn't be explained, and the description still previews the returned fields. Scope, source, cost and payment path are covered; only an explicit pointer to the iPhone sibling as the alternative 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 coverage is 100%, with the 'id' format and example and the 'country' default already documented in the schema. The description adds only that the key is an App Store track id, so 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?

It names a specific verb/resource ('Mac App Store app metadata ... by App Store id') and enumerates exactly what is returned (name, seller, version, price, rating, genre, link). The explicit 'Mac apps only' constraint separates it from the iPhone sibling dev_apple_app_store_iphone without the agent 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?

The 'Mac apps only' line gives clear selection context against the iPhone App Store sibling, and the pricing sentence signals this is a paid lookup path. There is no explicit 'use X instead when...' exclusion, but the platform constraint effectively routes the agent.

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