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

Annotations only cover readOnlyHint and openWorldHint, yet the description adds material operational detail: a metered price ($0.002 USDC per successful call), the x402 payment rails (Base, Solana, Arc), and the fact that failed calls are not charged. It also clarifies that ratings are the storefront's averages for the selected country, which prevents misreading the result.

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-loaded with what the tool does, then the operational constraints and price. The enumerated return-field list is slightly redundant given an output schema exists, but it is compact and every clause carries usable information.

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 4-param, zero-required tool with an output schema and safety annotations, the description covers mode selection, defaults, the 50-result cap, result semantics, and the payment/auth requirement. Nothing needed to invoke 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 coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: 'Country sets the storefront (default us)' and 'Ratings are the store's averages for that country' explain the semantic effect of the country parameter on returned data, which the schema text alone does not convey.

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 specific verbs and resources: 'Searches the App Store (iTunes Search API) by keyword, or looks up one app by its numeric id.' It also names the exact data returned (name, developer, bundle id, price, rating, etc.), so an agent can distinguish it from near siblings like package_search or github_search.

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 clearly distinguishes the two modes (keyword search vs. single-app lookup by id) and implies the id path is the alternative to q. It does not explicitly state when NOT to use it versus other store/search tools, but the context is unambiguous.

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