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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds value by enumerating the returned metrics, which matters because there is no output schema, but it omits behavior such as how the daily series is windowed, whether missing days are zero-filled, and any account-level prerequisites for the api_key.

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?

A single front-loaded sentence listing the resource and the returned fields with zero filler. It is terse to the point of being a fragment rather than a sentence, but no wording is wasted.

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?

Because there is no output schema, the description usefully names the metrics returned, which covers the biggest gap. However, for a 3-parameter tool it leaves the days parameter unexplained and provides no usage context relative to sibling read tools, so it is only adequate rather than complete.

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 67%: ad_id and api_key carry descriptions, but days (integer, 1-90) has none in the schema and the description never explains it. The phrase 'daily series' faintly implies the window concept but gives no default, upper bound, or granularity, so the description adds essentially nothing beyond the schema.

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 resource (one ad) and specific output (delivery totals plus a daily series of impressions, clicks, visits, spend), so an agent can tell it is a metrics-read tool. It does not explicitly contrast with the sibling get_ad, which presumably returns ad configuration rather than delivery, so differentiation is inferred rather than stated.

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?

There is no when-to-use statement, no mention of the days parameter's effect, and no routing to or from alternatives such as get_ad or list_ads. An agent can guess the intent from the title, but nothing in the description guides selection or exclusions.

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