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

Goes well beyond the readOnlyHint/openWorldHint annotations: it warns that YouTube truncates the description, that subscriber counts are rounded (with an example), that the locale is English, and it discloses the exact pricing model ($0.002 USDC per successful call via x402 on Base/Solana/Arc) plus the fact that failed calls are not charged. That is precisely the cost and data-fidelity context an agent needs before invoking a paid tool.

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-loaded with the core purpose and return fields, then caveats, then price. Dense but every clause carries information; the only mild bloat is the parenthetical example of a rounded subscriber count, which could be trimmed.

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 values needn't be explained, yet the description still summarizes the payload and flags its quirks (truncated description, rounded subs). Combined with the pricing disclosure, an agent has everything required to decide and invoke 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 coverage is 100% and the schema already specifies 'without @, e.g. TED'. The description's '@handle' reference is consistent with that but adds no new format or validation detail, so the baseline of 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 ('YouTube channel public details by @handle from the channel page') and enumerates exactly which fields come back (id, name, description, subscriber count, video count). Nothing about it could be confused with the sports/stats siblings, which all cover different platforms.

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?

Explicit scoping is given: 'public page data; English locale; no per-video stats', which tells the agent what this tool will not return. It stops short of naming an alternative tool for per-video or non-English data, so it's clear context without full routing guidance.

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