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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description's job is to add semantics — and it does: it defines the exact date window (excludes today), defines which conversion type is counted (primary/bid-relevant, matching the 'Conversions' column), and notes the additive property across campaigns. It does not discuss limits on data volume or freshness beyond the day boundary.

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 sentences, front-loaded with the metric list, then the time-window rule that matters most for correct invocation. No filler, though the conversions-definition sentence is dense and could be split for readability.

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 an output schema present, the description need not explain return shape, and it covers the two things the schema does not: the reporting window semantics and the workspace scoping rule. An agent has everything required to call this correctly.

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%, so the description must carry both parameters — and it does: 'days' is defined as N complete days ending yesterday (today excluded), and 'workspace' is explained as the client workspace slug, optional when only one workspace exists. Only the default value of 7 is left to 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?

States a specific resource (campaign performance) and enumerates the exact metrics returned (Impressions, Clicks, Cost, CTR, CPC, Conversions). An agent can distinguish this campaign-level report from ad-level or keyword-level siblings by the metric scope, though the description never names those siblings explicitly.

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?

Usage is implied rather than stated: the time-window rule ('N vollständige Tage bis gestern, heute nicht enthalten') and the note that summing all campaigns yields account totals give a sense of when the tool applies. There is no explicit guidance on when to prefer ads_ad_performance, ads_keyword_performance, or ads_device_performance instead.

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