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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds real behavioral context beyond them: the full-library cross-brand scope, the mandatory show_ad_carousel follow-up, the {ad_id, page_id} reference format, and cross-platform carousel mixing. It does not state auth/rate-limit behavior, but the mandatory downstream-call workflow is substantive disclosure.

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 purpose and alternative-routing are front-loaded and tight, which is good. However, roughly 70% of the text is a verbose, partially repetitive carousel-placement protocol ('REQUIRED', 'at least once this turn', 'Never render just 2-3 ads', 'strictly point → its carousel') that is more about show_ad_carousel than about this tool, bloating the definition.

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?

An output schema exists, so return values need not be explained, and the description covers purpose, alternatives, filters, the mandatory downstream rendering step, and the zero-results edge case. It is complete enough for correct invocation; only auth/permission or pagination-context notes are absent.

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 14 parameters (query, country, status, media_type, date range, sort_by, search_type, etc.) are already documented in the schema. The description only restates the existence of 'optional country, status, media type, and date filters' and adds no syntax, defaults, or interaction rules beyond what the schema provides, so baseline 3 is correct.

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 gives a specific verb and resource (discover ads by keyword/topic, full Meta Ad Library) and explicitly distinguishes itself from a sibling by contrasting with get_meta_ads, which 'only returns ads from the brand's own page.' It also names a second use case (partnership/influencer ads via creators), so an agent can select it 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?

It states exactly when to use this tool ('without knowing a specific brand', influencer/partnership discovery) and names the alternative (get_meta_ads) plus the condition that separates them. It also gives explicit when-to-skip guidance for the downstream carousel call (zero ads returned), leaving nothing to inference.

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