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 the credit cost '(1 credit)' and confirms Shorts URLs are accepted, which is genuinely useful, but says nothing about failure modes for invalid/private URLs or whether the response is a single object.

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 tight sentence: scope first, returned fields second, cost last. Nothing is redundant and the credit note is placed where it does not obstruct scanning.

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?

For a read-only, one-parameter tool with no output schema, the description carries the essential facts: input domain and the shape of the returned metrics. Only edge-case behavior (errors, unavailable videos, whether channel data is included) is left uncovered.

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 single 'url' parameter is documented in-schema as a YouTube video or Short URL. The description repeats that domain without adding format details (full watch URL vs. youtu.be vs. ID-only). With one fully documented parameter, the baseline 3 applies.

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+resource: fetches one YouTube video or Short by URL, and enumerates the metrics returned (views, likes, comments, duration, tags). This clearly separates it from collection-level siblings like youtube_channel_videos or youtube_search, though it never names an alternative explicitly.

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?

There is no when-to-use guidance, no prerequisite (e.g., obtain the URL via youtube_search first), and no stated exclusions such as private, deleted, or age-restricted videos. An agent must infer invocation conditions from the name alone.

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