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

Annotations already declare readOnlyHint/openWorldHint/destructiveHint=false, so the safety profile is covered. The description adds real value beyond that: hard limits (20 keywords, 31 future days), that results are account timezone/currency scoped, and that forecasts are not guarantees.

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?

Three tight, front-loaded sentences with no filler; the read-vs-write disambiguation and the numeric limits are placed first. Slightly clipped telegraphic style ('Account timezone/currency') but nothing 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?

For a nested body with nine required fields, an openWorld tool with no output schema, the description covers scope and limits but omits what the forecast actually returns and how the bid/budget inputs shape it. Adequate minimum, not 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 description coverage is only 33%, and the description only gestures at a few fields (keyword count, date range, currency). It does not clarify match_type, language_id, geo_target_ids, or that max_cpc_bid_micros/daily_budget_micros are bid/budget inputs in micros, so it only partially compensates for the coverage gap.

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 ('Read a hypothetical manual-CPC keyword forecast') and rules out the write path ('never create a campaign'). The qualifier 'manual-CPC' and 'hypothetical' distinguish it from the reach/keyword-historical siblings, though those siblings are not named.

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?

The 'hypothetical' and 'never create a campaign' framing implies when this is appropriate (pre-campaign estimates, not actual performance), but it never names the alternatives such as google_ads_keyword_historical_metrics or google_ads_reach_forecast, which is the main routing ambiguity for an agent.

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