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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavior beyond that: default Collection and Num values, the 200 cap, that FullDetail triggers a bulk app-detail lookup, and that Lang applies only to that lookup. It stops short of describing pagination or rate-limit behavior, so it is strong but not exhaustive.

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?

Three tight sentences: purpose and defaults front-loaded, then behavioral attributes, then sibling routing. No filler, and each sentence carries distinct 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?

An output schema exists, so return-shape explanation is unnecessary. Given the read-only/openWorld annotations and the 100% schema coverage, the description supplies everything an agent needs to call this chart-listing tool correctly, including the Lang/FullDetail dependency.

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 meaning the schema does not: it clarifies the conditional relationship that Lang applies to the FullDetail lookup and that FullDetail performs a bulk detail fetch. That conditional dependency is meaningful semantic information beyond the flat parameter list.

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 ('Fetch ranked Apple App Store chart entries') plus the scoping axes (storefront, collection, optional category). It also explicitly distinguishes itself from appstore_search and appstore_collection, so an agent can route correctly without opening the 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?

Gives explicit when-to-use-others guidance: 'Use appstore_search for keyword matches or appstore_collection for an editorial collection.' The alternatives and the conditions that select them are named, leaving nothing to inference.

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