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

Annotations already declare readOnly/idempotent/non-destructive, so the extra detail that matters is the auth requirement ('requires the MCP_API_KEY bearer token') and the cost disclosure that breakdown 'runs a second, heavier aggregation.' 'Read-only' merely restates the annotation, and there is no mention of pagination or rate limits, keeping it just below the top band.

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 the capability and metrics, then the breakdown guidance and auth note in a logical progression; nearly every sentence earns its place. Minor waste in repeating 'Read-only' and the account-scoping already implied by the product parameter.

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?

No output schema exists, and the description fully compensates by enumerating the returned counters and the breakdown dimensions (referring hosts, channels, campaigns, countries, devices, per-day trend). Auth, scoping, and the optional expensive path are all covered, so an agent can call it correctly without further information.

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 100%, so the baseline is 3; the description's contribution is mainly rationale — that breakdown answers 'why' while plain counters cannot, and that period is meaningless without breakdown. It does not add format or matching behavior beyond what the schema already documents for `product` (substring match) and `period`.

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 ('Get visitor analytics for one of the connected account's products') and enumerates the exact metrics returned (views, unique visitors for 7d/30d/all-time, published/draft review counts). An agent knows precisely what it retrieves, though it never names a sibling tool to contrast against (e.g. get_visibility_score or compare_visibility).

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?

Gives an explicit decision rule for the optional heavy path: 'ask for the breakdown whenever the question is why traffic moved or which source is working,' with the counter-case that counters alone cannot diagnose a spike. It stops short of stating when to prefer this tool over sibling analytics tools, so no full alternative routing.

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