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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely new behavioral facts: the call is free, and the returned download URL expires after roughly an hour — the latter is important for an agent deciding how quickly to consume the URL. It does not describe error behavior for missing or deleted items.

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?

Very compact, front-loads the cost fact, then the one-line summary, then args and returns. No sentence is wasted, and the args/returns formatting is easy to scan.

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?

With no output schema, the explicit return field list (ok, generation, download_url, attachment_url) and the URL expiry note fill the gap well for a single-parameter read tool. Minor omissions remain: no mention of failure modes when the id is invalid or the item was deleted.

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% and the schema field already says 'The generationId from library_list', so the description's 'library_id: from library_list' adds no meaning beyond the structured field. Baseline 3 applies when the schema does the heavy lifting.

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 and outcome: retrieves one item from the WEB Library and returns a signed download URL. The 'library_id: from library_list' note implicitly distinguishes it from the listing sibling, though it never uses an explicit verb like 'fetch' or 'retrieve', leaving the action to be inferred from 'Returns'.

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 reference to library_list implies the required workflow (list first, then get by id), which is useful context. However, there is no explicit when-to-use versus when-not guidance, and nothing tells the agent how this differs from siblings such as library_share, song_from_library, or library_delete.

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