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

The annotations already cover the safety profile (readOnlyHint, openWorldHint, idempotentHint, destructiveHint=false), so the description isn't required to establish that this is a safe read. It still adds real value beyond them: cost (¥0.1 per call), billing only on success, and automatic refund on failure or empty results, which is critical for an agent deciding whether to retry. It does not disclose pagination limits or result-count caps, which is the main remaining behavioral gap.

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?

Four short sentences, front-loaded with purpose, then return value, then usage, then billing. Every sentence carries information, and nothing is enumerating redundant schema fields. Slightly dense pack of clauses in the last sentence keeps it from being maximally crisp.

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 read-only search tool with no output schema, the description covers purpose, return shape, downstream workflow, and cost model, which is most of what an agent needs. Missing are result-count/pagination behavior and any hint about what order_by accepts, which matter for a discovery tool used to build candidate sets.

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 100%, so the schema is nominally the source of truth, and the baseline is 3. The description adds nothing about parameter behavior, and it never mentions order_by; the schema's own description ("排序" - sorting) gives no valid values or default. The description could have clarified sort options but does not.

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 opens with a specific verb and resource ("搜索YouTube视频" - search YouTube videos), which immediately distinguishes it from the many bili_/douyin_/tiktok_ keyword search siblings on other platforms. It also states the return shape (video list with content ID and basic engagement data). It doesn't explicitly name other yt_* siblings, but it does point to detail/comment endpoints as the continuation, giving a reasonably clear boundary.

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 use cases are given: keyword monitoring, content discovery, and building candidate sets, plus a clear next-step route ("ID可继续调详情与评论接口" - the ID can be used to call detail and comment endpoints). It lacks explicit when-not-to-use guidance or a distinction from keyword search on other platforms, which keeps it from a 5.

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