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

Annotations already declare readOnlyHint=true and destructiveHint=false, so 'Read-only' adds nothing. The description does contribute behavior beyond the structured fields: the result is rendered as a visual card in the UI, and the default window is the last 30 days. It stops short of covering authorization needs or behavior when neither account nor folder resolves.

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?

Four short sentences, front-loaded with the purpose and return contents before the secondary details. 'Read-only' is redundant against the annotations, but nothing else 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?

With no output schema, the description carries the burden of describing returns and does so by listing the row fields. For an 8-parameter, zero-required read tool the remaining gap is the lack of routing guidance among the many google_ads_* performance siblings.

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 88%, so the enum params (detail, date_range, language) and the account/folder/date fields are already well documented. The description reinforces the default period but adds no syntax, interaction rules (e.g. folder vs account precedence), or format detail beyond the schema; baseline 3 applies.

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 names a specific verb and resource ('compare individual Google Ads ads') and enumerates the returned metrics (spend, conversions, cost per conversion, CTR, approval status, first headlines), which tells an agent what it gets. It does not, however, distinguish this from close siblings such as google_ads_ads or google_ads_performance, so the agent must infer the division of labor.

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?

'Use this to compare individual Google Ads ads' implies the ad-level comparison use case, and 'Default period: last 30 days' sets a baseline. There is no explicit when-not guidance and no named alternative for account-level or campaign-level performance, which is the main gap given the large sibling set.

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