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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description's 'This does not change assets or delivery' largely restates destructiveHint=false, and the 60-day cap is duplicated in the schema, so net new behavioral context is limited. It does usefully confirm single-workspace scoping.

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 with the operation and its scope front-loaded; no wasted preamble. The second sentence is mildly redundant against the read-only annotations, keeping it out of 5 territory.

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?

An output schema exists so return values need no explanation, and all four parameters are schema-documented. However, for a tool with nested filter/breakdown objects, the description omits the segmentation (filters) capability and pagination behavior entirely, and gives no hook for choosing it over sibling analytics tools.

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 already documents workspace_id, date_range, breakdowns, and filters in detail. The description adds nothing about parameter format, filter operators, or the 1-3 breakdown limit, so baseline 3 is appropriate.

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?

States a specific verb and resource ('Read viewer metrics'), plus scope qualifiers: one workspace, grouped by a breakdown field, ≤60 day range. This distinguishes it from aggregate-style siblings, but it never clarifies how it differs from insights_breakdown_data, the closest sibling with an almost identical name.

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 explicit when-to-use or when-not-to-use guidance and no alternative tool is named, despite a crowded analytics family (analytics_aggregated_data, insights_breakdown_data, viewer_analytics_data, retrieve_analytics). The 60-day limit hints at one selection condition but the agent must infer the rest.

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