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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, and the description is consistent with them ("read-only"). Beyond the annotations it adds two genuinely useful behavioral facts: monetary fields ending in `_micros` are millionths of the account currency, and returned columns are camelCase (e.g. `metrics.costMicros`). It does not mention pagination behavior or result-size limits beyond the `limit` param.

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?

The core action is front-loaded in the first sentence, followed by the scope list, then the two unit/naming conventions an agent must know to interpret results, then a single routing pointer. Every sentence carries information an agent needs; nothing is padding.

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?

An output schema exists, so return shape need not be explained, and the description still supplies the column-casing convention and micros conversion rule that the output schema alone may not make obvious. Account scoping is covered by "against one Google Ads account"; only rate limits and result-size behavior are left unaddressed, which is a minor gap for a read-only query tool.

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 all four parameters (customer_id, query, limit, login_customer_id) are already documented in the schema, and the description adds no per-parameter guidance such as when to set login_customer_id for MCC access. Baseline 3 applies when the schema carries the parameter burden.

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 verb and resource ("Run a read-only GAQL query against one Google Ads account") and then enumerates the resource families it reaches (campaigns, ad groups, keywords, search terms, conversions, budgets, change history). An agent can distinguish it from ads_list_fields (field discovery) and from the GA4 reporting siblings without opening the schema.

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?

Gives a clear usage context (any report, one account) and explicitly routes field discovery to the sibling ads_list_fields, which is a real alternative-selection rule. It stops short of stating when to prefer ads_audit_campaign or a GA4 report over a raw GAQL query, so it is not a full when/when-not treatment.

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