Estimate audience size

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Changes nothing' largely restates them rather than adding new information. The description does add the useful behavioral framing that this is a prospective reach estimate rather than a stored audience, but says nothing about result variance, latency, or minimum audience thresholds.

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 short sentences, front-loaded with the purpose, followed by compact inline examples that earn their space. The trailing example block is slightly terser than it could be but contains 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?

With six parameters, nested objects, and zero schema description coverage, the definition should do more: four optional parameters are undocumented and there is no note on what the estimate response contains beyond the existence of an output schema. It is adequate for the required parameter but incomplete for the full surface.

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 0% across six parameters, so the description carries real weight, and it correctly supplies concrete examples for targeting_spec and keywords shapes. However, ad_account_id, creative_types, product_group_ids and auto_targeting_enabled are left entirely unexplained in both schema and description, leaving the compensation partial.

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?

'Estimate how many people an ad group's targeting would reach' is a specific verb plus resource and clearly separates this tool from the creation/mutation siblings (create_ad_groups, get_audience). It does not explicitly name a sibling to contrast with, so it stops short of a 5.

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?

Mentioning 'targeting_spec as in ad group create' implies the pre-flight/validation workflow before creating an ad group, but there is no explicit when-to-use, when-not-to-use, or named alternative such as get_audience_insights. Usage is inferred rather than stated.

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