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

Annotations already declare a safe read operation (readOnlyHint=true, destructiveHint=false). The description adds substantive context beyond them: the values are relative indices rather than percentages or absolute search volumes, and the caller must preserve provider region IDs for downstream use. That interpretation guidance is valuable and not inferable from the 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?

Three short sentences, front-loaded with the purpose and immediately followed by the two facts most likely to be misread (relative index semantics, ID preservation). 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?

With no output schema, the description carries the return-value burden and does so by explaining that regional scores are relative indices and that region IDs come back and must be retained. The only remaining gap is pagination/response shape, which is minor for a read-only lookup.

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 50% and the description adds no parameter-level detail beyond implicitly tying the tool to the US market (matching the const 'US' on the market field). 'Preserve provider region IDs' concerns output rather than inputs. Baseline 3 applies since the schema documents the date and keyword constraints itself.

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 names a specific verb and resource ('relative keyword interest across United States regions'), which clearly distinguishes it from siblings like keyword_interest_history or keyword_interest_demographics. It doesn't explicitly name those siblings, but the resource and geography are concrete enough for an agent to match the tool to the request.

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?

Usage is only implied: an agent infers this is for comparing a keyword's regional popularity within the US. The caveat about relative indices warns against misusing the tool for absolute counts, which is useful, but there is no explicit when-to-use/when-not guidance or named alternative for country-level or demographic interest.

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