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

With no annotations provided, the description carries the full burden and does a good job: it discloses the 20-ads-per-call cap, that results are third-party sourced from Atlas Data, a 6-hour cache staleness window, and a 0.02 USD per-call x402 payment requirement — a real precondition for invocation. It stops short of stating failure modes or rate limits.

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?

Purpose and query modes are front-loaded in the first clause, followed by the field list and then operational facts (cap, provider, cache, price) in short compact sentences. The opening sentence is long but dense with no filler; only the field enumeration runs slightly long.

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 13-parameter tool with no annotations and no output schema, the description covers the important gaps: it describes what comes back, the result cap, the data source's trust level, freshness, and cost. The residual gap is guidance on the ambiguous filter parameters (sort, adType, mediaType) that the schema leaves as bare names.

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 baseline is 3. The description reinforces the two principal query modes (keyword vs. pageIds) and the 20-item output cap, but adds nothing about the opaque parameters whose schema descriptions are just the field name itself ('sort', 'mediaType'), leaving the agent without interpretive help there.

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 description gives a specific verb and resource ('Search the Meta (Facebook/Instagram) Ad Library'), names the underlying archive, and enumerates the returned fields (advertiser, ad text, creative format, landing page, platforms, dates, status, spend/impression ranges). That enumeration plus the platform qualifier separates it cleanly from the only adjacent sibling, linkedin_ads.

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?

'By keyword or advertiser page ID and country' tells the agent how to drive the tool, and the phrase 'public ad-transparency archive' implies the legitimate use case. But there is no explicit when-not guidance and the sibling linkedin_ads is never named as an alternative for LinkedIn ad data, so routing is left to inference.

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