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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: the grain (one row per SD campaign) and the freshness caveat that recent ~3 days may be incomplete. It stops short of documenting pagination/return limits, which the output schema likely handles.

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 sentences with zero waste: purpose and metrics first, then grain and freshness, then exclusions and routing. Everything is front-loaded and each 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?

With a 100% covered schema, an existing output schema, and annotations that carry the read-only profile, the description only needed to add scope, grain, freshness, and sibling routing — all of which it delivers. Nothing an agent needs to invoke it correctly is missing.

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% across all 10 parameters, so the schema fully documents limit, offset, sort, date defaults, filters, and diagnostic flags. The description adds no parameter-level syntax or format detail, so the baseline 3 is appropriate.

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 (Sponsored Display campaign performance) and enumerates the metric families returned (viewability, NTB, DPV, spend, sales, ACOS). It also names the sibling categories it is not (SP/SB, sales), so an agent can select it 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?

The description gives an explicit exclusion ("Do not use for Sponsored Products/Sponsored Brands or total product sales") and routes the agent to the matching campaign or sales tool. Both the when and the when-not are stated, leaving little to inference.

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