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

Annotations already declare readOnlyHint and openWorldHint, so the safety bar is low. The description adds real behavioral value by noting that enabling Platforms 'costs one extra upstream page fetch', a cost signal not present in annotations or schema.

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 the single-sentence purpose, then parameter guidance and the sibling reference. Information-dense and largely free of waste, though it duplicates several schema-described parameters.

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?

An output schema exists, so return values need not be explained, and the description covers purpose, identification, defaults, and the sibling alternative. A minor gap is that the Lang parameter is never mentioned, but the schema covers 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 the schema already documents all six parameters. The description restates Country and Platforms and the id/app_id choice but adds little syntax or format detail beyond what the schema provides, so the 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 ('Returns normalized app metadata from the App Store lookup API') and clarifies it identifies an iPhone, iPad, or Mac App Store listing. It also names the sibling it is not (appstore_search), so an agent can distinguish it from search tools without opening schemas.

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?

Explicitly routes the agent to appstore_search for searching, and states the id/app_id requirement. It lacks an explicit 'when not to use' beyond that, but the context for calling it (to look up a known app) is clear.

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