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

Beyond readOnlyHint/openWorldHint, the description adds genuinely useful behavior: credit costs per mode, the warning that repeated requests may purchase the same data again, login-only ads being unavailable, and the null-firstShown pitfall. However, the pricing story is internally inconsistent ('1 credit per request' vs. 'at least 10 Nexscope credits'), which leaves the agent uncertain about actual cost.

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 text is badly bloated: the core paragraph appears verbatim twice, followed by stitched fragments ('Google Ad Library Company Ads API View Pricing ...') and a trailing sentence that merely restates the schema's get_ad_details description. The useful content is front-loaded but buried under duplication.

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 10-parameter read-only lookup with a fully documented schema and annotations, the description covers the essentials an agent needs: cost per mode, data-availability caveats, and the null-date handling rule. Pagination behavior via cursor and output shape are unaddressed, but no output schema exists and the schema documents cursor.

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 100%, so the baseline is 3, but the description does add meaning beyond the schema for get_ad_details (it switches to the individual-ad source rather than merely enriching the same response) and for the domain/advertiser_id lookup keys. Other parameters (topic, region, platform, cursor) are left entirely to 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?

The opening sentence is a specific verb+resource statement ('Fetches public company ads by domain or advertiser_id') and it distinguishes the two retrieval modes (default list vs. get_ad_details individual-ad source). It never names a sibling tool such as social_google_ad or social_google_ad_library_advertisers_search, so differentiation is implicit rather than explicit.

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?

Clear context is given for when to stay on the cheap default (1 credit) versus opting into get_ad_details (25 credits, individual-ad source), plus the caveat that login-only ads are unavailable. There are no explicit exclusions or pointers to alternative siblings, so it stops short of full when/when-not guidance.

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