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

Annotations already cover read-only/idempotent/non-destructive, and the description adds what they cannot: paid-plan gating, 1 credit per page of 25 rows, empty pages free, a 2,000-call daily cap on the derived family, and that all 11 Amazon marketplaces are covered. This is exactly the kind of cost/quota context that prevents surprise failures.

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?

Every sentence carries information and the key constraint (kinds) is front-loaded, but the whole definition is one dense run-on paragraph mixing kind enumeration, usage, cost and marketplace coverage. A short bulleted split would scan faster at this length.

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 an 8-parameter, 5-mode discovery tool with no output schema, the agent gets modes, ranking semantics, pagination size, marketplace scope, cost model and next-step tools. Nothing needed to call it correctly is missing.

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?

Goes well beyond the schema by mapping ranking fields to each kind (e.g. top_brands by buy-box days / sellers / control_score / asins / revenue / amazon_share, top_sellers by brands / buybox_days / asins / revenue) and by explaining window, direction, parent_id and category_id in context. It stops short of giving the literal accepted `sort` string values per kind, leaving the agent to translate prose field names into enum-like values.

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 (ranked LISTS from Logimu's observations) and then enumerates all five kinds with exactly what each ranks. It is unambiguously distinct from the lookup-oriented siblings (brand, seller, category) which it explicitly contrasts against.

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 an explicit when-to-use rule ('USE WHEN the user wants to DISCOVER brands, sellers or categories rather than look one up'), lists concrete triggers (sourcing leads, brands under seller pressure, biggest resellers, hot categories), and names the follow-up tools for drilling in.

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