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

Beyond the readOnly/openWorld annotations, the description discloses three high-value behaviors: the data comes only from public page data (provenance), the hidden 'view email' address requires CAPTCHA and is deliberately not returned (a concrete capability limit that prevents wasted calls), and the call costs $0.002 USDC via x402 with failed calls free (billing semantics). These are exactly the facts an agent cannot infer from structured fields.

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 what is returned, then the CAPTCHA limitation, then the price — each of the three sentences carries distinct, non-redundant information. No filler or restatement of the tool name.

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 need not be detailed further, and annotations cover the safety profile. Combined with the provenance and pricing disclosures, an agent has everything needed to decide and 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?

With one parameter at 100% schema coverage, the schema already documents the handle format ('@YouTube', 3-30 chars, allowed characters). The description adds no handle-specific guidance such as URL handling or case sensitivity, so a baseline 3 is appropriate.

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 names a specific verb and resource — pulling the YouTube channel About page (description, country, subscriber/view/video counts, external links, emails) — and states the exact data source as YouTube's public page data. This is clearly distinguishable from sibling tools like social_youtube (video-centric) or social_youtube_channel_search (discovery), since the emphasis on About-page/contact fields is unambiguous.

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?

Usage is implied (contact/creator email lookup) but never explicitly stated: there is no 'use this when you need X, use Y instead' framing, despite siblings like social_youtube_channel_search, social_instagram_contact, and social_contact_info being plausible alternatives. The CAPTCHA caveat does implicitly define a boundary of what this tool can do, but that is a capability limit, not a routing guideline.

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