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

Annotations already declare readOnlyHint and openWorldHint, and the description adds value beyond them: the ~20 result cap, the absence of video lists and exact subscriber counts, and the billing model ($0.002 USDC per successful call, failures not charged). These are real behavioral facts an agent cannot get from the schema or annotations.

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?

One dense but front-loaded sentence listing content first, then limitations, then cost — an efficient ordering. It is long, but nearly every clause carries information the agent needs; the trailing pricing sentence is a slight tail rather than waste.

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 return-value explanation is optional, and the description still previews the returned fields. Combined with the documented limitations and pricing, an agent has enough to call this correctly; only sibling routing is missing.

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% for the single 'topic' parameter, so the schema already defines it fully, including the 'education' default. The description restates the default rather than adding new semantics; 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 and resource: channels returned from a topic search on YouTube, with an explicit default topic and result count. However, it does not differentiate itself from the very similar sibling social_youtube_channel_search, leaving the agent to guess which one applies.

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 sets scope ('first page of about 20', 'no video lists or exact subscriber counts') which implies when it fits, but never says when to prefer social_youtube_channel_search or social_youtube_search instead. Usage is inferable rather than stated.

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