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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior: the exact 30-minute lookback window and the dimensions returned, which the annotations cannot express. Auth requirements and rate limits are not mentioned, but the marginal gap is small.

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 sentences with zero filler: the first front-loads what the tool returns and its time window, the second carries the use cases. Nothing is repeated from the title or schema.

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?

For a single-optional-parameter, read-only tool with no output schema, the description discloses the window and the metric dimensions an agent needs to decide to call it. Property resolution is already handled by the schema, so nothing material is missing.

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% and the single property parameter is fully documented there, including accepted id formats and optionality. The description adds nothing about the parameter, so baseline 3 applies.

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 resource and scope: realtime active users in the last 30 minutes, with named breakdowns (page/screen, country, device, minutes ago). The 30-minute window implicitly separates it from ga4_overview and ga4_report, but no sibling is named explicitly, so the differentiation is inferred rather than stated.

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?

"Use it to check a launch, a campaign or that tracking works after a change" gives concrete, actionable when-to-use context rather than vague guidance. It does not say when this is the wrong choice or point to a non-realtime alternative such as ga4_report for historical data.

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