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

Annotations already cover the safety profile (readOnly, openWorld, non-destructive), and the description adds genuinely useful behavior: caching semantics, per-call cost, and the provenance of contact fields. However, it contradicts itself on cost ('at least 10 Nexscope credits' vs '1 credit per request'), and bundles an unrelated data-removal notice, which makes the operational picture muddier rather than cleaner.

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 purpose is front-loaded, but the text is heavily polluted with vendor boilerplate: a support-email removal notice, duplicated marketing lines ('YouTube Channel Details API View Pricing Get YouTube channel details...'), and a raw markdown docs link. These sentences do not help an agent call the tool and dilute the parts that do.

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 usefully enumerates the return payload (profile fields, counts, join date, tags, linked accounts, country, email, store links) and covers the caching behavior, which is enough to call it correctly. The remaining gap is failure-mode behavior and the identifier-required rule, given that the schema marks all four parameters optional.

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 0%, so the description carries the full burden and mostly meets it: it names the three interchangeable identifier inputs and explains cacheMaxAge in concrete terms (age threshold, 0 vs 1 credit, 'cached'/'cached_at' in the response). It still omits the channelId format constraint (^UC...{22}) and what happens if multiple or zero identifiers are passed, both of which the schema leaves unexplained.

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 first sentence uses a specific verb and resource ('Retrieves comprehensive YouTube channel profile data') and enumerates the returned fields, so an agent immediately knows this is the channel-level profile lookup. It does not, however, name or contrast the adjacent siblings (social_youtube_channel_videos, social_youtube_channel_search, social_youtube_channel_playlists), so the boundary with those tools is only implied.

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 says the tool accepts a channelId, handle, or full channel URL, which is real input guidance, and it explains the cacheMaxAge trade-off (cached = 0 credits vs live = 1 credit). It never states when to prefer this tool over channel_search or channel_videos, nor that exactly one identifier should be supplied, leaving the selection decision mostly to inference.

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