Compare two periods

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful behavioral context by specifying that results include overall totals plus biggest gainers and losers by clicks, and that the previous range defaults to the equal-length period immediately before the current range. It does not cover auth requirements, rate limits, or failure behavior, so it adds some but not rich 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 sentences, both carrying useful information. The primary purpose is front-loaded, and the default-previous-range behavior follows immediately with 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?

For a 9-parameter tool with nested filters, 33% schema description coverage, and no output schema, this description is thin. It gives the high-level comparison behavior and previous-range default, but omits meaningful guidance on filters, top, type, and the full return structure, which an agent would need to invoke the tool 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 33%, so the description must compensate. It usefully explains the default behavior for previousStartDate and previousEndDate, which the schema leaves undocumented, and references the dimension parameter. However, it does not explain top, type, filters, or the interplay between startDate/endDate defaults beyond a brief note, leaving substantial parameter semantics uncovered.

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 uses a specific verb and resource: it 'compares performance between two date ranges by a dimension' and states the return shape ('overall totals plus the biggest gainers and losers by clicks'). It is clear what the tool does, but it never names or contrasts itself with relevant siblings such as search_analytics or detect_drops.

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 description explains what the tool does but gives no explicit when-to-use or when-not-to-use guidance. It does not say when an agent should prefer this over search_analytics, detect_drops, or page_performance, nor does it mention prerequisites such as needing a property from list_sites.

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