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

Annotations already establish read-only and non-destructive behavior. The description adds meaningful context beyond that: it compares against the previous period, notes that totals match the Search Console UI, and caps recommendations at 3. It also labels the tool as 'Read-only' again, slightly duplicating the annotation but reinforcing the behavior.

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 with no filler: the purpose is front-loaded, the returned content is clearly listed, and the alternative routing is given. Every phrase earns its place.

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 simple read-only tool with 2 well-documented parameters and no output schema, the description tells the agent what it returns, how it compares periods, and when to choose a different tool. Nothing essential for selecting and invoking it correctly is missing.

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 100%, so both `site` and `days` are already fully documented in the input schema. The tool description adds no param-specific semantics, but it doesn't need to; the schema carries the burden and does so thoroughly.

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 clear directive ('Start here') and explicitly enumerates what is returned: clicks, impressions, CTR, average position, page gainers/losers, and recommendations. It distinguishes itself from the sibling search_performance, so an agent can tell which tool to use for an overview vs. a custom breakdown.

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?

It explicitly states when to use this tool ('for any "how is my site doing" question') and names the alternative for other cases ('For custom breakdowns use search_performance'). This leaves no ambiguity about the tool's role among the many siblings.

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