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

Annotations only declare readOnly/openWorld, while the description adds substantial behavior: result cap (up to 40 ads), the returned fields (format, first/last shown dates, preview and Transparency Center links), the Google ad-count estimate, and a detailed pricing/rate-limit model (5 free calls per IP per day, then $0.01 USDC per result via x402 on Base, no charge when no ads are found). This is well beyond what annotations provide.

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?

The content is front-loaded and every sentence carries real information (scope, output, pricing). It is dense and runs long in the middle listings, but there is little pure filler, so only mild trimming would be warranted.

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 paid, read-only external API with an output schema, the description supplies the critical extras an agent needs: cost/rate limits, the no-charge guarantee for empty results, region filtering, and the shape of the return (cap, formats, dates, links). Nothing essential for correct invocation 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% and both parameters are documented in-schema, so the baseline is 3. The description restates the region filter and enum list already present in the schema and adds no new syntax or format meaning for 'domain', so it neither compensates nor exceeds the schema.

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 ('Google Ads transparency API: is a company running Google Ads, and what does it advertise?') plus the exact lookup key (advertiser domain). It is clearly distinguishable from siblings such as get_company_profile or company_footprint_check because it names the data source (Google Ads Transparency Center) and the returned entity 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?

Gives clear use context ('competitor research, ad-spend signals and sales personalization') and hints at the charging model, but never routes the agent to or away from a specific sibling tool, nor states explicit exclusions. Clear context without alternatives lands at 4.

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