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

No annotations are provided, so the description carries the full burden; it does add genuine behavioral facts — cost ('Free'), a fallback search order (index, then YouTube), and endpoint equivalence. It omits rate limits, behavior on no-results, and whether api_key is needed for the YouTube tier, which leaves meaningful gaps for an unannotated 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?

Two short sentences, cost and source order front-loaded, zero filler. The telegraphic fragment style ('Channels by name or handle: ...') borders on unclear, but nothing is wasted.

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 described, and the core search behavior is covered. Against three parameters at 0% schema coverage and no annotations, however, the description should say more about api_key requirements and result limits.

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 0% across three parameters. The description only implies that 'q' is a name or handle; it says nothing about 'limit' (default 20, max 50) or the optional 'api_key' and what it unlocks. Two of three parameters are undocumented in both schema and description.

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 states a concrete resource and search inputs ('Channels by name or handle') and reveals the two-tier strategy ('shared index first, then YouTube's own channel search'). It never names the closely related siblings search_index, get_channel, or similar_channels, so an agent must infer how this differs from them.

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?

'Free' is a real cost signal that helps an agent choose this over paid alternatives, and the fallback ordering implies this is the general-purpose channel lookup. But there is no explicit when-to-use vs. when-not and no named alternative (e.g. use get_channel for a known ID).

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