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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: Klaviyo is an owned channel with spend=0 by design and an is_owned_channel marker, and revenue is what each platform reports for itself (self-attributed). These details go beyond the schema and annotations and help set expectations about data semantics.

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 sentences with no fluff. The first sentence packs the core function, scope, and key metrics; the second explains a critical edge case (Klaviyo spend=0). Information is front-loaded and every clause earns its place.

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?

Given the output schema exists and the annotations cover safety, the description is largely complete: it lists platforms, metrics, grouping options, and the Klaviyo owned-channel caveat. It could go slightly further by noting how rows are aggregated or whether zero-spend platforms are excluded, but these are minor gaps and the core information needed to call the tool correctly is present.

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 parameters are already fully documented. The description reiterates the group_by values (platform, campaign, country) and platform list, but adds no new parameter-level semantics. Baseline 3 is appropriate because the schema does the heavy lifting and the description contributes little beyond what is already structured.

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 states a specific action ('Get'), a specific resource ('paid and owned channel performance'), and enumerates the exact platforms and metrics involved. It clearly distinguishes this tool from siblings like get_channel_roas or get_revenue_breakdown by covering multiple ad platforms, including owned Klaviyo, and listing metric types.

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 implies usage (when needing cross-platform ad performance across the listed channels) but does not explicitly state when to use this tool versus alternatives such as get_channel_roas or get_date_range_summary. It does not name any sibling or provide exclusions, leaving routing largely to inference.

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