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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful behavioral context beyond that: the two media types have separate genre ID spaces and IDs are not interchangeable across the chart tools, which is a real correctness constraint an agent must respect.

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 short sentences, each load-bearing: what the tool returns, the required parameter, then the downstream ID routing. The constraint is front-loaded and there is no filler.

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 structure needn't be described. Given the low parameter count and annotation coverage, the description supplies everything needed to call it correctly: the required media choice, the storefront scope, and how to use the resulting IDs with the chart siblings.

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%, and the schema already documents both `media` (book or audiobook, separate ID spaces) and `country` (two-letter code, default US). The description reinforces that media is required but adds nothing about `country` or accepted values beyond what the schema states, so it sits at the baseline-3 level.

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 ('List the complete public genre navigation') scoped to 'one Apple Books storefront', which cleanly separates it from siblings like apple_books_charts, apple_books_search, and apple_books_author. An agent can identify the operation 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?

Explicitly says media is required and names the two valid values, and then routes the agent onward: audiobook IDs to apple_books_audiobook_charts, ebook IDs to apple_books_charts. That is concrete next-step guidance, though it doesn't state when to call this tool versus apple_books_charts directly (e.g., 'call this first to discover genre IDs').

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