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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safe read-only profile is covered. The description adds the returned metrics and device granularity, but does not disclose date-range defaults, whether missing dates span all time, or any auth/rate-limit behavior—minor gaps given the annotation coverage.

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, front-loaded with the returned metrics and granularity, followed by the intended use. No filler and every clause contributes to selection or invocation.

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?

The description adequately conveys what the tool returns and its scope, and annotations cover the safety profile. However, with no output schema and low parameter coverage, more detail is needed on date handling and the campaign/property relationship for an agent to call it confidently.

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 only 25% (only the required 'property' parameter is documented in the schema). The description does not compensate: it never explains the optional startDate/endDate format, defaults, or the campaign parameter other than implying one campaign may be selected. This leaves three of four parameters semantically underspecified.

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 states a specific set of metrics (Cost, clicks, CTR, conversions, CPA) and the exact dimension (per device: mobile, desktop, tablet) and scope (account or one campaign). This clearly distinguishes it from generic siblings like ads_campaign_performance or ads_geo_performance without needing to open 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?

The phrase 'Basis for device bid adjustments' implies the intended use case, but there is no explicit when-to-use guidance, no alternatives named, and no exclusions. The agent must infer that this tool is chosen over other performance breakdowns when device-level optimization is needed.

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