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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real value beyond them: a 2-hour observation window and the warning that streams ending immediately before the query may be unconfirmed. It stops short of describing result ordering or volume, but the staleness disclosure is exactly the kind of behavior an agent needs and cannot get from annotations.

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 dense and front-loaded with the purpose before the parameter clauses, and every clause contributes information. It reads as a run of telegraphic fragments without visual separation between purpose, params, and caveats, which slightly slows parsing.

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 3-parameter, all-optional search with annotations but no output schema, the definition covers scope, all parameter semantics, and freshness limits. The remaining gaps are the return shape (no output schema exists) and sibling differentiation against search_live_streams.

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%, so the description carries the full burden and does: keyword is a partial match across title/channel/description capped at 200 chars, category is a YouTube category ID with a concrete example (20=ゲーム), and limit is constrained to 1–10 with default 5. All three parameters get meaning the bare schema does not provide.

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 phrase "最終確認時点で配信中のライブを検索" gives a specific verb (検索) plus resource (配信中のライブ) with a temporal qualifier, so the agent knows this returns currently-active streams only. It never mentions the sibling search_live_streams or explains how the two differ, so the agent must infer the distinction from the name alone.

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?

There is no explicit when-to-use/when-not-to-use guidance and no named alternative among the nine siblings. Usage is only implied through the freshness caveats ("2時間以内の観測のみ", "検索直前の終了は未確認"), which tell the agent when the data is trustworthy but not why to pick this tool over search_live_streams.

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