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

Goes well beyond the annotations (which only say readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false) by disclosing the 21-day shared cache behavior, that fresh:false is not cache-only and retries can repeat billed provider work, that no Scan allowance is consumed, and that null means unavailable rather than zero. This is precisely the billing/side-effect context the readOnlyHint=false annotation leaves ambiguous.

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?

Dense but well front-loaded: the returned metrics lead, followed by usage, then execution semantics. The semicolon-chained behavioral clauses are slightly sprawling, but nearly every sentence carries information an agent needs to call it correctly.

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 billed, cached, open-world batch lookup with an output schema present, the description covers everything an agent needs — scope, defaults, cache/billing semantics, null handling, and the aggregate-trend return shape ('not full monthly history'). Return-value explanation is correctly delegated to the output schema.

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 already 100%, so the baseline is 3, but the description adds real non-obvious meaning: omitted/GLOBAL region targets the US rather than worldwide volume, language defaults to en, keywords are trimmed and deduplicated case-insensitively, and fresh:false is explicitly not cache-only. This exceeds what the schema alone conveys, though it doesn't restate every field.

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+resource ('Search metrics for a batch of keywords') and enumerates the returned metrics (volume, CPC, competition, difficulty, intent, trend), immediately distinguishing it from siblings like get_seo_backlinks, get_seo_page_audit, and get_seo_search_results. An agent knows exactly what this returns without opening the 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?

Gives clear task-oriented guidance ('size demand for terms, gauge how hard they are to rank for, see whether interest is rising or falling'), which brackets when to reach for it. It stops short of naming an alternative sibling or stating when not to use it, so it falls just below the explicit routing bar.

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