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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 real context beyond that: the cookie/auth requirement, the conditional favorites behavior, and the default "videos only" scope for feed. It stops short of describing pagination semantics or result volume.

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?

A single dense sentence front-loads the verb, resource, and auth prerequisite, then enumerates modes with semicolons — zero filler. It is somewhat packed, but every clause carries a distinct fact.

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 six parameters, no output schema, and a multi-mode dispatch, the description covers the mode semantics and the auth prerequisite well. Return shape and pagination behavior are left implicit, though cursor/next is documented in the schema, which is a reasonable division of labor.

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 67%, and the description compensates by defining every `what` value and the folder_id presence/absence branch, which the schema only labels as "收藏夹 ID". It says nothing about page or cursor beyond what the schema already documents.

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 states a specific verb and resource ("读取已登录账号的数据") and then enumerates all five values of the `what` enum with their meanings (me/watch_later/favorites/history/feed). An agent can distinguish this from bili_user (other users) and bili_watch_later_edit (mutation) 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 gives a clear prerequisite (BILIBILI_COOKIE must be configured) and spells out the branch condition for favorites: without folder_id it lists folders, with folder_id it lists contents. It does not explicitly name alternatives such as bili_user or bili_watch_later_edit or state when not to use this tool, so it falls short of full routing guidance.

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