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

Annotations already establish this is a read-only, non-destructive, closed-world read, so the description legitimately focuses on semantics. It adds real behavioral context the annotations cannot: the grain is one row per ranked ASIN and each row carries two distinct rank grains (subcategory vs top-level department). It stops short of describing pagination or freshness behavior beyond what the schema notes.

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 core purpose, then grain details, then the exclusion rule. Three sentences, no filler, and each sentence carries distinct information (what, structure, what-not).

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 an output schema present and 100% schema description coverage, the description needn't document return format or parameters exhaustively. It supplies the higher-order context an agent needs — result grain, the two rank grains, and scope limits — so nothing essential is missing for correct invocation.

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 lacks: it explains that sales_rank/sales_rank_category is the most specific subcategory rank while main_category_rank/main_category is the headline department rank, which disambiguates the sort_by enum values and the max_rank filter. It does not address limit/offset/include_raw_rows/include_diagnostics.

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 (latest Best Sellers Rank across catalog ASINs) and enumerates the returned fields (rank, category, title, brand). It also draws a clear boundary against keyword-rank and velocity tools, so an agent can distinguish it from siblings like get_keyword_ranks and get_sales_velocity without opening a 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 gives a when-not-to-use rule (keyword rank tracking, actual sales velocity) and names one concrete alternative, get_sales_velocity. The other redirect, 'ranking tools', is left vague even though siblings get_keyword_ranks and get_current_rank exist, which weakens the routing guidance slightly.

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