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

With readOnlyHint=false, the description usefully explains the state side effect: 'the latest read is kept for grow', which is why the tool is not read-only. It also discloses the external dependency and auth requirement (App Store Connect with Admin role) and that the call is free, which annotations alone 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?

Front-loaded with the ranking rationale and tiers, then the input/fallback rules, then cost/retention. It is dense but each clause carries information; the middle ranking sentence is long but not padded.

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 no output schema, the description does the necessary work by describing what each result contains ('the App Store Connect locale to write and its language') and the ordering logic. The only missing piece is the meaning of `appId`, which is also absent from 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 coverage is 50%: `locales` is documented in the schema, and the description reinforces its meaning by naming its source (fastlane/metadata/<locale>/ folder names) and the fallback semantics. `appId` is explained in neither the schema nor the description, leaving a real gap.

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?

The description states precisely what is returned: 'The countries the app's listing could open next, best first', including the ranking tiers. The resource (countries for App Store listing expansion) is distinct from siblings like app_metadata or app_keywords, though the differentiation is implicit rather than by naming a sibling.

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 gives clear conditional input guidance (pass `locales` from fastlane folders when App Store Connect is not connected, otherwise the listing counts as storefront-language only) and a prerequisite (Admin role). However, it never says when to use this tool versus the many adjacent planning tools (launch_targets, listing_targets, plan), so routing remains inferential.

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