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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds non-obvious behavioral detail: that device=watch with section=arcade returns a 400, and the default values (Country=us, Section=main). This exceeds annotation coverage with concrete runtime facts.

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?

Purpose is front-loaded, which is good, but the body duplicates itself: the Device enum is listed once as '`device` enum: ...' and again as 'Device: ... Allowed values: ...', and Country's ISO-2/default note appears twice. The blending of prose and schema-fragment style makes it denser than it needs to be.

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. The description covers purpose, all four parameters, defaults, the watch/arcade error, and the sibling alternative — enough for correct invocation. The only gap is the undocumented Lang parameter, which is left entirely to the schema.

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 every parameter. The description largely repeats that content (the Device enum, the Country ISO-2 note) rather than adding syntax or format detail. The only genuine additions — what 'main'/'arcade' mean and the watch/400 case — are marginal, so 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+resource ('Returns the curated editorial shelves from ... App Store landing pages') and anchors it to the real-world artifact (apps.apple.com's device switcher). It explicitly distinguishes itself from appstore_editorial_category (category-scoped) and notes the vocabulary differs from appstore_search's platform values, so an agent can route 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?

Gives a clear alternative route: 'Use appstore_editorial_category to retrieve an App Store category-scoped editorial page.' It also clarifies the section semantics (main vs arcade) and the incompatibility (watch has no Arcade). It stops short of a full when/when-not statement, but the positive context and the named sibling make selection unambiguous.

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