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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower, and the description still adds real behavior: keys present in only one comparison period show zeros in the other, the default period ends at the last synced date because Search Console lags ~3 days, and every response states the period used. It omits how rows are capped/paged beyond the schema's limit field.

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 resource definition, then output fields, then sort semantics, then the noise-avoidance tip — a sensible order with little waste. It is dense with parentheticals and the trailing bilingual 'Por país.' earns nothing, keeping it just below a 5.

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 carries the important load: it enumerates the returned row fields and the comparison-derived fields, and explains default date behavior. Filtering parameters (brand, device, query, pageContains, country) are covered only by the schema, which is adequate given 100% coverage, but the description does not tie them into the country-breakdown use case.

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 a 3 would be defensible, but the description genuinely adds meaning the schema lacks: it spells out what 'position (lowest first)', 'growth (largest click gain)' and 'decline (largest loss)' actually sort by, and explains the prev*/change field family that the comparison parameter produces. It adds nothing about limit, query, device, brand, or pageContains beyond what the schema already says.

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 resource (countries, ISO-3166-1 alpha-3, lowercase) scoped to 'one property over the period', which is a concrete verb+resource+scope statement. It implicitly occupies the country-dimension slot next to query_devices and query_top_queries but never names or contrasts them, so sibling differentiation is left to inference.

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?

There is no explicit when-to-use / when-not-to-use statement or routing to alternatives among the many sibling query tools. The only usage advice is embedded in the sort discussion ('For ctr/position use minImpressions >= 20 to avoid noise'), which is parameter guidance rather than tool-selection guidance.

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