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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the description's real contribution is the cost model — "Billed per 20 results of depth" — plus the 40-result ceiling, which is high-value disclosure an agent cannot get from annotations. It stops short of describing ranking behavior, rate limits, or empty-result handling.

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 tight sentences: the return shape is front-loaded and the limit and billing note follow. Every clause carries information an agent would otherwise have to guess.

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?

With no output schema, the field enumeration (video ID, title, channel, views, publish date, duration, Short flag) does the work a return-value doc would. The only gap is guidance on query semantics and what happens if fewer than max_results match.

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 75%: country, language, and max_results all carry their own defaults and formats in the schema. The description's "Up to 40 results" merely restates the schema maximum and adds nothing about query syntax, quoting, or locale interactions, so the baseline 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?

The description gives a specific verb-plus-resource ("YouTube search results for a query") and enumerates the returned fields, so an agent knows exactly what comes back. It does not, however, explicitly contrast itself with the sibling youtube_video, which an agent would need for a detail fetch rather than a ranked listing.

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 statement of when to use this versus youtube_video, google_serp, or google_trends, and no prerequisites or exclusions. Usage is only inferable from the tool name and the "for a query" phrasing.

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