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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered by structured data. The description adds behavioral value beyond annotations by disclosing that placement_modifiers are included when scoped to campaigns and that include_shared_campaigns can roughly double product-scoped results. It does not describe output metrics or date defaults, but the disclosed behavior is meaningful.

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?

The description is three sentences with no filler: front-loaded core purpose, then scope modes, then a response-nuance note. Every sentence earns its place, and the structure lets an agent quickly identify what the tool does and which parameters matter.

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-parameter tool with no output schema, the description covers the main selection modes, the default behavior, and a notable response field, which is enough to make a reasonable first call. It does not specify default date windows or the full metric set, so it is not fully complete, but the core usage context is 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?

Schema description coverage is 64%, and the description adds useful semantic context for scoping parameters by mapping asin/parent_asin/sku to product-level campaigns and explaining group_by_campaign. However, it adds little for start_date, end_date, period_days, campaign_id, or campaign_name_contains, which are not well described in the schema either. The description partially compensates for the coverage gap but does not fully carry the parameter documentation burden.

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 and resource: 'Get performance breakdown by placement type' from SP placement data, and names the placement types (Top of Search, Product Pages, Rest of Search). It also distinguishes the tool by enumerating account, campaign, and product scoping modes, separating it from sibling breakdown tools like ppc_match_type_breakdown or ppc_ad_type_breakdown.

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 explicitly explains when to use each scoping mode: ACCOUNT level default, CAMPAIGN level via campaign_id/campaign_name_contains, PRODUCT level via asin/parent_asin/sku, and per-campaign via group_by_campaign=true. It does not name sibling alternatives to exclude, but the scope guidance is clear and actionable enough for an agent to select this tool appropriately.

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