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

Annotations cover the safety profile (readOnlyHint, destructiveHint=false), so the description is not burdened there. It adds genuinely useful behavior: a cap of 6 distinct ads, an EU/UK-only scope that the result self-reports, filtering of unrelated pages, and a 1-credit cost. Those extras are not in the structured fields.

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?

Front-loads the core action and cap, then the constraints, then cost. Mostly tight, though 'and the result says so' is slightly loose phrasing and the filtering clause is dense.

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?

No output schema exists, so the description carries the return-value burden and does so reasonably: it discloses the 6-ad cap and that unrelated pages are named but not shown. Credit cost and platform scope round it out, leaving only minor gaps like ad record fields.

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 schema already documents brand, country, and competitor. The description's 'brand-name search' and EU/UK notes add marginal framing but no syntax or format detail beyond the schema, so the 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?

States a specific verb and resource ('Active ads from the official Meta Ad Library API') and pins the platform, which naturally separates it from the sibling competitor_ads_google. An agent can tell what it fetches and from where without opening the schema.

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 an applicability constraint ('EU/UK delivery only') and notes it is a brand-name search, but never states when to pick this over competitor_ads_google or what happens outside EU/UK. Usage is implied rather than guided.

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