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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the description's value-add is the data-semantics warning that unreported days are ABSENT, not zero — a genuinely important quirk that prevents wrong trend inference. It adds no auth, rate-limit, or pagination context, so it falls short of the top score.

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 dense sentences, zero filler, with the core resource definition front-loaded and the critical ABSENT-not-zero caveat placed last for emphasis. 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?

With no output schema, the description does carry return-value burden, but it already enumerates the metrics returned (spend, sales, clicks, ACoS) and flags the missing-day behavior. The main residual gap is any mention of result shape or ordering, which is minor for this tool.

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 the schema already documents 'days', 'campaign_id', and the marketplace/currency scoping. The description adds no parameter format or syntax beyond that, so the baseline 3 applies.

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 (per-day ad spend, sales, clicks, ACoS) and frames it against the sibling capability it replaces ('a 30-day rollup cannot'). An agent can distinguish this from get_ads_overview purely from the description.

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?

Gives explicit triggers — pacing, pinpointing the day a change took effect, validating a trend before claiming it — which tell the agent when this series is the right choice. It stops short of naming a sibling to avoid, though the rollup contrast functions as an implicit alternative.

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