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

Annotations already establish readOnly/non-destructive/openWorld safety. Beyond that, the description discloses two genuinely useful behaviors: the API-level limitation on competitor data and the default 30-day window. It stops short of describing pagination, granularity options, or return shape.

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-loads the resource and metrics, then the disambiguating NOTE, then the default window. Three tight clauses, 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?

No output schema exists, yet the description names the metric family returned, which is the key informational need. The remaining gap is parameter documentation and return structure, minor for a simple read-only metrics tool.

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 0% for 3 parameters. The description only covers the date-range default ('last 30 days'), leaving startDate/endDate format and customerId entirely undocumented in both schema and description. It partially compensates but far from fully.

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 impression-share metrics per campaign') and enumerates the exact metrics returned (share, top, absolute-top, lost to rank vs budget). The caveat that this is your account's share and not the competitor-domain Auction Insights report cleanly separates it from any competitor-comparison sibling.

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 implied by the metric list and the NOTE clarifies what the tool cannot do (no competitor Auction Insights), which is a useful when-not. However, it never routes the agent among sibling reporting tools (e.g. get_campaign_performance, run_report) or states prerequisites such as needed customerId/permissions.

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