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 value by specifying that it returns 'channel metrics and identifiers' intended for 'snapshot baselines', giving context on output content and purpose beyond the annotations. It does not discuss pagination, errors, or identifier exclusivity, but the additional note about snapshot baselines is a meaningful behavioral disclosure.

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?

The description is two sentences long, front-loads the verb and resource, and states the return purpose without redundancy. Every word contributes to understanding the tool's function and intended use.

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 fetch tool with a simple schema and no output schema, the description covers the main purpose and return type. It mentions metrics and identifiers, which suffices for most use cases. A minor gap is the lack of explicit guidance that exactly one identifier is needed, but this is implied by 'by channel id, handle, or URL'. Overall, the definition is adequate for an agent to call correctly.

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 description coverage is 100%, with each parameter (url, handle, channelId) described individually. The description adds the framing that these are alternative identifiers ('by channel id, handle, or URL'), which implies interchangeability, a nuance not explicitly in the schema. However, it does not clarify that at least one is required, nor does it specify behavior if multiple are provided. The added value is modest over the schema's already descriptive parameter comments.

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 uses a specific verb 'Get', names the resource 'YouTube channel', and specifies the scope 'details by channel id, handle, or URL'. It clearly differentiates from sibling tools like youtube_channel_videos_list or youtube_channel_shorts_list, which are about videos, by focusing on channel metadata. The mention of returning 'channel metrics and identifiers for snapshot baselines' adds purpose specificity.

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?

The description implies when to use this tool: when you have a channel id, handle, or URL. It distinguishes from list-type siblings by focusing on 'details' rather than videos or shorts, but does not explicitly name alternatives or state when not to use it. The context is clear, but exclusions are left to inference.

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