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

The annotations already declare readOnlyHint=true and openWorldHint=true, so the read-only and open-world nature are known. The description adds one piece of behavioral context: 'use cursor when paginated', which is useful. However, it doesn't elaborate on return format, error conditions, or any other behavioral traits. Given the annotations carry much of the load, a score of 3 is appropriate—it adds value without overloading.

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 description is two concise sentences with zero fluff. The primary purpose is front-loaded in the first sentence, and the second sentence covers input options and return behavior. Every word serves a purpose, making it optimally concise and structured.

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?

Given the low parameter count (10 but all optional) and thorough schema descriptions, the tool description covers the essential information: purpose, primary input options, and pagination. It doesn't mention the implications of providing both pageId and companyName or neither, but that's a minor gap. The openWorldHint annotation indicates results may be non-exhaustive, which the agent should know. Overall, it's complete enough for an agent to call correctly.

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 all 10 parameters are documented in the schema. The tool description merely restates the dual input option ('Accepts a page id or company name'), which is already present in the schema descriptions for pageId and companyName. No additional semantic depth is added, justifying the baseline score of 3.

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 clearly states the verb ('List') and resource ('ads a company or Page is running in the Facebook Ad Library'), which is specific and unambiguous. It doesn't explicitly differentiate from the sibling facebook_adLibrary_ads_search_get, but the function's scope (list all ads for a given company/Page) is distinct enough that an agent could infer the difference from the name and description combined.

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?

The description offers no guidance on when to use this tool versus alternatives such as facebook_adLibrary_ads_search_get or facebook_adLibrary_companies_search. It states that it accepts a pageId or companyName, but doesn't explain when one would choose this list endpoint over a search or a company lookup. This leaves the selection decision to the agent based solely on the tool name.

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