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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description still adds genuinely new behavior: result ordering (newest first), the transcript-readiness field, paging support, and filter scope. It does not state the default page size or what happens past the end of the library, but the value added beyond annotations is real.

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?

Two sentences, front-loaded with purpose and returned fields before the usage note. The tail of the second sentence ("or to show what is in there at all") restates the first clause and could be dropped, a small redundancy in an otherwise tight 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 the field enumeration in the description is optional but harmless, and the read-only annotations cover safety. What is missing is coverage of the platform filter and paging defaults, both of which an agent needs to use the tool fully. Complete enough to call correctly, not complete enough to exploit all four parameters.

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 50%: offset and title_contains are documented in-schema, while limit and platform have no descriptions. The description compensates partially by mentioning paging and a title/channel filter, but it never mentions the platform filter or the default/maximum page size, leaving two parameters unexplained in both places. Partially compensates, so a 3 rather than a 2.

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 (list the videos the user saved), the ordering (newest first), and the exact fields returned. The closing clause distinguishes it from a query-based sibling by scoping it to browsing with no search query, so an agent can separate it from search_my_library without opening either 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 explicit use condition: browse the library when there is no search query. That implicitly routes query-based cases elsewhere, but the alternative sibling (search_my_library) is never named, so the agent must infer which tool to pick for the search case. Clear context, no explicit exclusion.

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