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

Annotations already cover read-only, open-world, and idempotency hints. The description adds valuable return-shape information: per-campaign rows plus ad-group, keyword, and ad-level breakdowns, and a previous-period comparison. It stops short of rate limits or pagination, but adds clear behavioral context beyond annotations.

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 short paragraphs, front-loaded with purpose and return shape, then date defaults and custom-range guidance. Every sentence earns its place and the structure is easy to scan.

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?

No output schema exists, so the description appropriately explains the returned data and previous-period comparison. It does not mention pagination or row limits, but for a read-only reporting tool the essential context is present.

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 75%, with startDate, endDate, and periodDays documented in the schema. The description reinforces ISO date format and default 30-day behavior, but does not explain brandId or the interaction between explicit dates and periodDays.

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: fetch Google Ads performance data for a brand over a date range, including named metrics and breakdown levels. This distinguishes it from account-level or keyword-suggestion siblings even without naming them.

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?

Implies usage by describing the previous-period comparison and date defaults, but does not explicitly say when to choose this over siblings like get_account_summary or when not to use it. The date guidance is useful but parameter-focused rather than tool-routing guidance.

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