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

Beyond the annotations (read-only, idempotent, non-destructive), the description discloses materially important behaviors: the per-row billing at $0.18 (up to 20 rows, header excluded), that 4xx/5xx responses are not charged, and that the response is semicolon-delimited text rather than JSON. These details directly influence invocation and parsing decisions and are absent from the annotations and schema.

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: the first states the core purpose, the second covers billing constraints, and the third flags the response format. Every sentence earns its place and the most important decision-relevant facts (what it returns, what it costs) are front-loaded.

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?

For a read-only keyword lookup with an output schema present and annotations covering the safety profile, the description covers the critical invocation facts: cost model, row cap, error-charging policy, and response format. Minor gaps remain (e.g., behavior on empty results, whether the row cap is per phrase), but nothing blocks correct invocation.

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?

The description itself adds no parameter-level detail, but schema coverage is 100%: both `phrase` (with URL-encoding guidance) and `database` (with default `us`) are already documented in the schema. This matches the baseline of 3 where the schema carries the parameter-semantics burden.

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 opening sentence names a specific output ('Domains and URLs currently running Google Ads'), the query basis ('for a keyword'), and the live status of the data. This clearly separates it from the organic counterpart get_semrush_organic_results among the siblings, and the title 'Paid Results' reinforces the distinction.

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?

No explicit when-to-use or when-not-to-use guidance is given, and no alternative tool is named. The intended use case is only implied by the contrast between 'Paid Results' and the sibling get_semrush_organic_results. An agent could infer the choice, but nothing in the description states it.

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