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

Annotations already cover safety (readOnly, non-destructive, openWorld, non-idempotent), and the description adds genuinely new context beyond them: the return payload ('first and last shown dates and days running'), the credit cost of 1, and the upstream data source. Idempotency nuance and any rate-limit or empty-result behavior are left unstated, which keeps it off a 5.

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 with zero filler: capability first, accepted inputs second, return shape and cost last. The negative constraint ('No keyword search') is placed where it is most useful, right after the input forms it qualifies.

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?

No output schema exists, and the description compensates by naming the returned fields, so an agent knows what to expect. For a three-parameter read tool this is nearly sufficient; only the limit/pagination behavior and result ordering remain unclear.

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 67%, above the threshold where the schema carries the burden. The description repeats the target formats already present in the target property's own description and says nothing about 'limit' (max 100) or the region default, so it adds little meaning beyond the structured fields.

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 ('List a competitor's Google ads'), names the source (Google Ads Transparency Center), and enumerates the surfaces covered (Search, Display, YouTube). The 'No keyword search' clause is what separates it from the keyword-based ad_radar_spy sibling, so an agent can pick correctly without opening a 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?

Tells the caller what input forms are accepted (domain or advertiser id) and explicitly excludes the keyword-search use case, which implicitly routes that traffic to the sibling tool. Missing an explicit 'use X instead for keyword lookups' sentence and any note on when to pick this over ad_radar_spy or ad_radar_evaluate, 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.