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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so safety is covered. The description adds the aggregation grain (campaign + ad group) and a data-freshness caveat ('recent ~3 days may be incomplete') that the annotations do not convey. It stops short of describing result behavior, but that is partly covered by the output schema.

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?

Two sentences, front-loaded with the use case, then exclusions. No filler, no restatement of the tool name, and the freshness caveat is placed adjacent to the grain it qualifies.

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, return values need no explanation, and the description still covers scope, grain, freshness, and routing. For an 11-param read-only reporting tool, nothing material 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?

Schema description coverage is 100% across all 11 parameters, so pagination, date patterns, sort enums, and filter semantics are already documented. The description adds no parameter-level detail beyond echoing the metric list that maps to sort_by. Baseline 3 is appropriate when the schema carries the load.

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?

Specific verb ('drill') plus resource ('Sponsored Products performance ... from campaign to ad group') with the exact metric set (spend, sales, ACOS, ROAS, CTR, CPC, CVR) and grain. An agent can distinguish it from get_campaign_performance (coarser) and the keyword/search-term tools without opening any 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?

Explicit exclusions with named alternatives: 'Do not use for bidded keyword/target or customer search-term analysis; use get_keyword_performance or get_search_terms.' Combined with the stated grain, the agent knows both when to reach for this tool and when to route elsewhere.

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