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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: 'Leitura pública, sem auth' (auth need) and the return shape {count, items} with the item fields (title/url/posterUrl/durationSeconds/orientation/loopFriendly/tags). It does not discuss rate limits or pagination behavior, so not a 5.

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-loaded with the resource and sub-actions, and every clause carries information about use or parameters. It is dense and somewhat run-on within a single long sentence with parenthetical lists, which costs a little readability, but there is little wasted text.

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 9-param, 3-action tool with no output schema, the description covers the list return fields and the per-action intent well, and even the categories return content (moods/usos). The only minor gap is the exact return shape of get by videoId, which is left implicit.

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 baseline would be 3, but the description adds real meaning beyond the schema: it lists the concrete mood categories, maps orientation to aspect ratios with intent (vertical=9:16 for shorts, horizontal=16:9), and explains loopOnly='fundo que repete limpo'. That is additive value over the already-complete schema.

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 resource (stock clip/B-roll catalog ready on CDN, downloadable, free/internal) and enumerates the three sub-actions (categories/list/get) with what each returns. It explicitly distinguishes itself from the sibling sapiens_video by positioning itself as ready-made B-roll rather than generation.

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?

Explicitly routes the agent: 'Use pra puxar B-roll pronto em vez de gerar via sapiens_video', naming the alternative and the condition. It then gives concrete use cases (page background/atmosphere, B-roll in the /sapiens:movie ffmpeg pipeline, first/last frame) and hints at orientation/loopOnly choice for shorts vs page backgrounds.

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