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

Annotations already establish the safe read-only, closed-world profile, and the description adds real behavioral context beyond them: the default window ends 3 days back because newest days are attribution-incomplete, end_date overrides it for reporting, and placement_modifiers appear when scoped to campaigns. It does not discuss pagination or rate limits, but is strong on the operational caveats that matter.

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-loads the core purpose before diving into scoping modes, and every sentence carries substantive information with no filler. It is dense and paragraph-heavy for a 14-parameter tool, but nothing is wasted.

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 14-param, zero-required tool with no output schema, the description covers scoping, the default date window, and a note on response contents (placement_modifiers), which is enough for an agent to call it correctly. Minor gaps remain around return shape and how the access-scoping flags interact, but the essentials are present.

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?

With 14 parameters at 64% schema coverage, the description meaningfully supplements the schema by mapping parameter groups to scoping modes (campaign-level vs product-level vs per-campaign) and explaining the default date window and the end_date override. It clarifies group_by_campaign's row-per-campaign output, adding value over the terse schema descriptions.

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 ('Get performance breakdown by placement type') and enumerates the placement values (Top of Search, Product Pages, Rest of Search) from SP placement data. It distinguishes itself from the modifier-focused sibling by noting placement bid modifiers are returned only as part of the response, letting an agent differentiate without opening schemas.

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 lays out the four available scopes (account default, campaign via campaign_id/campaign_name_contains, product via asin/parent_asin/sku, and per-campaign via group_by_campaign=true), which tells the agent when each mode applies. It stops short of naming competing siblings (e.g. ppc_placement_modifiers, ppc_ad_type_breakdown) as alternatives or stating when-not to use it.

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