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

Annotations already declare the read-only, idempotent, closed-world, non-destructive profile, so the safety bar is covered. The description adds genuine behavioral context: the upstream source (Amazon's spCampaigns daily reports) and the critical null-semantics rule that absence means no report rows rather than zero share — a common misinterpretation for share metrics. It does not describe pagination or refresh cadence.

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 metric definition, then the data source, then usage, then the caveat — a sensible ordering. The metric enumeration is slightly dense but each item earns its place by defining what the tool returns.

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 usefully enumerates the returned measures and explains the empty-result case, which is the main ambiguity for a share metric. An agent has enough to call it and interpret the response; only return shape details (row granularity, sort order) are absent.

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?

Only one parameter (days) with 100% schema description coverage including default 30 and max 90, so the schema carries the load. The description contributes nothing about the window, so baseline 3 is appropriate.

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 — Top-of-Search impression share and placement stats per campaign — and names the data source (Amazon's own spCampaigns daily reports). The enumerated metrics (share of eligible top-of-search impressions, top-of-search impressions, clicks, spend vs total impressions) make it clearly distinguishable from siblings like get_ads_daily_series or get_ads_search_terms.

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 concrete usage contexts: 'visibility questions — why impressions are flat, whether a campaign shows at the top of search.' It also supplies interpretation guidance for empty results. It stops short of naming which sibling to use for adjacent questions (e.g., overall campaign performance), so it is not a full when/when-not routing rule.

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