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

Annotations already establish readOnly/openWorld/non-destructive, so the bar is lower, and the description adds real value beyond them: it discloses billing behavior ('billed like an API request; one unit per result page') and advises keeping max_results modest. It stops short of stating pagination mechanics or rate limits.

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 purpose, then return shape, then filtering and billing. The field enumeration is long but each item is informational; the billing sentence earns its place. Minor verbosity in the field list.

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 description admirably enumerates the returned fields, and it covers filtering, pagination, and cost. The only notable gap is the unexplained `proxy_country` parameter, which an agent cannot infer.

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 baseline is 3. The description restates the `type` and `sort` option sets and notes pagination behavior for `max_results`, but adds no syntax or semantics beyond the schema and says nothing about `proxy_country`.

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?

Opens with a specific verb+resource: 'Searches YouTube for `query` and returns the results as JSON.' It also enumerates the returned fields, clearly separating it from the sibling youtube_transcript (search results vs. transcript).

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 rather than stated: it explains how to filter with `type`/`sort` and how to control volume with `max_results` and a billing caution. There is no explicit guidance on when to pick this over siblings like youtube_transcript or google_search, nor any exclusions.

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