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

Annotations already mark it read-only and open-world, and the description adds meaningful behavior beyond them: non-deterministic results, non-subscribable nature, per-item credit cost, and the extra_fetch cost ceiling up to page size. This is solid added context, though the return shape isn't described.

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?

Front-loads the core purpose and keeps sentences purposeful. The cost statement is slightly redundant ('Costs 1 credit per item fetched, up to the page size. Costs 1 credit'), which costs a point but doesn't obscure meaning.

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 description carries the burden and mostly succeeds: it covers region scope, credit costs, and the pagination cursor implicitly via schema. It stops short of describing the returned item shape, but for a trending-list tool it is largely complete.

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 75%, so the schema already documents most parameters including extra_fetch's cost note. The description reinforces region scoping and extra_fetch behavior but adds little beyond the schema, and cache_max_age remains unexplained in both.

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 scope up front ('Trending shorts... by region') and explains that it reads the ranked Shorts surface rather than the retired global Trending feed. This clearly separates it from siblings like youtube_channelShorts or youtube_search.

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 useful context on what the tool returns and warns that results differ per request and are not subscribable, but never states when to prefer it over alternatives such as youtube_channelShorts or youtube_search. Usage is implied rather than prescribed.

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