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

Annotations already establish the safe-read profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description still adds real value beyond them: it discloses the error-envelope behavior on missing schema ('silent-fail signature') and the attribution-footer obligation, both of which affect how the agent must handle output.

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 purpose and Brand Account caveat are well front-loaded, but roughly half the text is a generic data-accuracy contract that is not specific to geography retrieval and would apply to any tool. That boilerplate dilutes a definition that could be a third the length.

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 carries the return-value burden; it covers error behavior but never describes the shape of the geography result (e.g. country/dimension and metric fields). The accuracy contract and footer rule add policy context, yet a caller still cannot anticipate the successful response payload.

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 50%: video_id and channel_id are documented in the schema, while start_date and end_date are bare. The description reinforces channel_id (Brand Account targeting) and mentions the single-video case, partially compensating, but says nothing about the date range parameters, which is the uncovered half.

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 specific verb and resource ('Get geographic viewer breakdown') and scopes it to the authenticated channel or a single video. The geographic dimension is what distinguishes it from get_my_youtube_analytics, though no sibling is named explicitly.

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?

It gives one concrete routing rule — pass channel_id for Brand Accounts because channel==MINE will not resolve — which is genuinely useful. However it never states when to reach for this tool versus get_my_youtube_analytics or get_my_youtube_video_analytics, leaving the primary selection decision to inference.

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