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

Annotations already mark readOnlyHint=true and destructiveHint=false, and the description does not contradict them. It adds a useful detail by specifying the return shape ('array of daily data points') and included metrics, but it doesn't explain how date windows behave when period_days vs start_date/end_date are provided, or how missing days are handled.

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 tight sentences: the first states the purpose and output, and the second lists the metrics and the intended use case. There is no filler, redundancy, or unnecessary detail.

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?

The description is adequate for a simple read-only trend endpoint, but with 12 optional parameters and no output schema, it doesn't explain filter behavior, date defaults beyond the schema's period_days setting, or how this compares to ppc_period_comparison and ppc_account_summary. The return values are partially described, making this only minimally 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 roughly 67%, and most scoping parameters already have meaningful descriptions. The tool description adds no parameter-level semantics, such as how sku, asin, and campaign_id filters interact or the default lookback behavior, so parameter understanding relies on 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?

The description uses a clear verb ('Get'), a specific resource ('day-by-day metrics'), and states the output: an array of daily data points with cost, sales, ACoS, clicks, and impressions. It doesn't explicitly contrast with sibling tools like ppc_period_comparison or ppc_conversion_funnel, but the daily time-series framing makes its role clear.

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 description says the tool is 'for trend analysis' and 'useful for spotting spikes, dips, and patterns over time,' which provides a clear when-to-use context. It doesn't mention alternative tools or explicitly state when not to use it, so it stops short of full routing guidance.

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