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

Annotations already cover read-only, idempotent, non-destructive and closed-world behavior, so the bar is lower. The description adds genuinely useful context beyond them: every field is derived server-side from the User-Agent at collection time, implying the values reflect collection-time data and are not re-parsed retroactively, plus a cost/first-party signal.

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?

Three short clauses, front-loaded with the resource and dimension before the provenance note and the cost tag. Nothing is repeated and no sentence can be dropped without losing information an agent uses for selection.

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 still conveys what the result represents (a device/browser/OS breakdown) and where the data comes from, which is enough for a three-required-param read tool. It could have hinted at the shape of the rows or any grouping thresholds, but the gaps are minor.

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% for all three parameters (projectId, startDate, endDate), including format and ordering constraints, so the schema does the heavy lifting. The description adds no parameter-level meaning at all, making the baseline 3 the correct score.

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 names a precise dimension triple (device/browser/OS breakdown) scoped to a project's own tracking snippet, which clearly separates it from sibling analytics reads like get_web_analytics_sources, get_web_analytics_top_pages and get_web_analytics_summary. It stops short of naming those siblings, so the differentiation is inferable rather than explicit.

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 statement, and no alternative is named. The 'FREE, first-party' tag hints at a preference over third-party/paid sources such as the GA4 tools, but this is an implication the agent must construct, not guidance.

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