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

Annotations already declare readOnlyHint=true, openWorldHint=true, non-destructive, so the safety profile is covered. The description's main added behavioral fact is that KD/intent are null for Google Ads-served countries, which is duplicated in the locationCode schema text, so the description contributes little beyond structured data.

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 with the capability and the use case front-loaded, no filler. The final null-metrics caveat is useful but slightly redundant with the schema.

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 read-only hydration tool with a full output schema and 100% parameter coverage, an agent has everything needed to invoke it correctly. The description is complete enough, though it could have named a sibling to route discovery queries elsewhere.

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%, so the schema already documents every parameter including defaults, the 700 cap, and the Google Ads country caveat. The description adds no syntax or format detail beyond what the schema provides, so the baseline of 3 applies.

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 (hydrate) plus the exact metric set (volume, KD, intent, CPC, competition, monthly trends) and the batching limit of 700. This distinguishes it from discovery-oriented siblings like research_keywords or get_domain_keyword_suggestions.

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?

Gives a clear context: use it to score candidate or known keywords, and calls out the Search Console striking-distance use case. It implies rather than names the alternatives (e.g. that discovery of new keywords belongs to research_keywords), so no explicit when-not guidance.

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