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

Annotations already declare readOnly, idempotent, and non-destructive behavior, and the description adds useful context beyond that: it uses two independent public models, returns a range rather than a single value, and flags UK/DE as rough scalings. No contradiction exists between the description and annotations.

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?

Two sentences, front-loaded with the main function and output, followed by scope and an optional multiplication behavior. Every clause adds information; there is no repetition of the title or fluff.

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?

For a low-complexity, read-only estimation tool, the description covers inputs, supported marketplaces/formats, output type, and optional royalty scaling. There is no output schema, so the description's statement that it returns an estimated range of units per day and per month is sufficient, though exact response structure is not detailed.

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 0%, so the description must carry parameter meaning. It conveys bsr ('Best Sellers Rank'), format ('Kindle Store or print'), marketplace ('Amazon.com ... UK/DE'), and royaltyPerSale ('Optionally multiplies by royalty per sale'). It does not specify currency or exact units for royaltyPerSale, but the core semantics are recoverable.

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 a specific verb ('Turns ... into an estimated range of units per day and per month') applied to a clear resource: an Amazon Best Sellers Rank. It defines what the rank is, distinguishes from a general sales calculator, and separates it from sibling tools like royalty_calculator by focusing on rank-to-sales estimation rather than royalty computation.

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?

The description gives clear usage context: it works for Amazon.com Kindle Store or print, and notes that UK/DE results are rough scalings. It does not explicitly name alternative tools or state when not to use it, but the scope and limitations are clear enough for an agent to select it appropriately.

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