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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and external-data behavior are covered. The description adds genuine context beyond that by characterizing the collection as editorially curated rather than algorithmic, which shapes how results should be interpreted. It stops short of noting freshness or result size, keeping it at 4 rather than 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?

Two sentences, zero waste: the first establishes what the tool returns, the second is pure routing. Front-loaded with the purpose before the sibling alternatives.

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 parameters, an output schema present to describe return values, and annotations covering the read-only/open-world profile, nothing an agent needs to call this correctly is missing. The only added requirement, differentiation from siblings, is fully handled.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly avoids inventing parameter talk that would confuse a parameterless call.

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 (Fetch) and resource (Bilibili's curated must-watch video collection), and immediately distinguishes itself from three named siblings (bilibili_popular, bilibili_ranking, bilibili_weekly). An agent can select this tool without opening any 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?

Explicitly routes the agent: use this for the curated must-watch collection, use bilibili_popular for popularity-ranked videos, bilibili_ranking for charts, bilibili_weekly for weekly picks. When-to-use and alternatives are both spelled out with no inference required.

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