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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered; the description adds useful behavior on top: newest-first ordering and that every item carries its permanent URL. The caveat that library files are not necessarily on a page is genuinely valuable domain context an agent could not infer from annotations, though nothing is said about what happens at the limit boundary or when a library is empty.

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?

Three sentences, no filler: what is returned first, then how to use it, then the disambiguating caveat. The parenthetical hero-video example earns its place by naming the sibling workflow it feeds, and nothing repeats the annotations or schema.

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 read-only five-parameter tool with full schema coverage and no output schema, the definition covers return shape (assets plus permanent URL, newest first) and the key conceptual distinction between library contents and page contents. Only the behavior at the limit boundary or on an empty library is left unstated, which is a minor gap rather than a blocking one.

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 five parameters, including the asset_type enum and the limit default of 50, are already documented in the schema. The description reinforces the newest-first ordering that governs limit and its remark that library files may be unused on any page shades the meaning of the unused flag, but it never explains filter semantics directly, so the baseline of 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 names a specific resource and scope: the images, videos and files in one site's media library, returned newest first with a permanent URL. The listing verb is implicit (the opening is a noun phrase) and it doesn't differentiate itself from the several other read tools nearby (list_brand_assets, list_connected_assets, search_brand_library), though it does separate itself from plan_image_regeneration.

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 gives an explicit when-to-use (find an uploaded photo or clip to place, with a concrete hero-video example feeding apply_hero_pattern) and an explicit when-not, routing the agent to plan_image_regeneration for 'what a design actually shows.' It leaves the brand-media and connected-asset alternatives unaddressed, so a 4 rather than a 5.

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