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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description goes well beyond annotations: it states totals are returned ONLY for additive metrics, lists excluded categories (market share, rates, CTR, CPC/CPA, unique counts), and defines avg precisely as the unweighted mean of returned rows rather than a population KPI.

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?

Three sentences, front-loaded with the core purpose. Each sentence earns its place: the first states what is computed, the second defines total eligibility, and the third clarifies the avg semantics. No filler.

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 single-parameter aggregator with annotations covering safety and no output schema, the description is complete. It specifies which statistics are computed and the rules that govern them, so an agent has what it needs to invoke the tool correctly.

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 coverage is 100%, so the single rows parameter is already fully documented as 'The rows array from a previous query result.' The description reinforces that these are numeric result columns but adds no syntax, format, or structural detail beyond what the schema provides; 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: compute descriptive statistics for numeric result columns, and distinguishes its treatment of additive vs. non-additive metrics. It does not name sibling tools or explicitly contrast itself with alternatives, so it is clear but lacks sibling differentiation.

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?

No explicit when-to-use or when-not-to-use guidance. The schema description 'The rows array from a previous query result' and the metric rules imply this follows a query, but the agent receives no routing guidance versus siblings like significance_check or search_performance.

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