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

Annotations already cover the safety profile (readOnlyHint, openWorldHint), so the bar is lower. The description adds genuinely useful behavioral detail: the fixed 30-minute activity window, the country breakdown, and the fact that the `days` parameter is inert for this tool.

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 short sentences, zero waste, and the defining constraint (realtime / 30 minutes) is front-loaded before the caveat.

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, but the description states the return dimension (breakdown by country) and the temporal scope, which is sufficient for an agent to invoke it correctly. Only slight gap is the absence of any mention of the optional `property` default behavior.

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 the single `property` parameter, so the schema already carries that meaning; baseline 3 applies. The description adds no parameter syntax or default details of its own.

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: active users in the last 30 minutes, broken down by country. This clearly distinguishes it from the list_* snapshot siblings, which report historical aggregates rather than a realtime view.

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?

The word 'Realtime' and the note that it 'ignores the `days` window entirely' tell the agent when this tool is the right choice versus the windowed list tools. It does not explicitly name an alternative or a when-not condition, so it stops short of a 5.

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