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

Annotations already declare this a read-only, open-world, non-destructive operation, so the bar is lower. The description still adds real behavioral context the annotations cannot convey: no authentication or browser session is required, and billing is '1 credit per result' with failed items free, which is decision-relevant for an agent. It omits pagination/truncation behavior, which keeps it at a 4.

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?

A single sentence, front-loaded with the verb and resource, then the output fields, then a short pricing note. Every clause carries information and nothing is padded.

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?

With no output schema, the description compensates by listing the ad fields returned, and the rich input schema covers all parameters. What is missing is return-shape nuance such as per-search paging or what happens when maxResults truncates a search, which matters for a 1000-entry batch tool.

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 keyword vs. Page ID distinction, country codes and active status are already fully documented in the schema. The description only echoes that a search is 'by keyword or advertiser Page ID' without adding syntax, exclusivity rules, or limits beyond the schema. Baseline 3 applies.

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 Facebook Ad Library') and enumerates the returned payload fields (ad text, images, videos, CTA, run dates, platforms), so an agent knows exactly what it gets. It does not name or differentiate itself against any sibling tool, which is the only thing keeping it from a 5.

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?

It states the two ways to drive a search (keyword or advertiser Page ID) and asserts 'No login, no browser', which implies a low-friction context. However, it never says when to pick this over an alternative source or what conditions make it unsuitable, leaving usage largely implied.

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