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

Annotations already declare a safe, idempotent, closed-world read, so the description's added context is what matters: it defines the counting semantics ('counted as they come', last 5 minutes, not visitor-days) and, with no output schema present, enumerates the returned fields (site, time zone, live_visitors, window_minutes, at) and notes UTC. No contradiction with annotations.

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 core question ('How many are on a site now') and every sentence is informational, including the return-shape sentence that compensates for the missing output schema. It is dense and the 'who is there now, not visitor-days' clause slightly restates the preceding definition, keeping it from a 5.

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-parameter read tool with no output schema, the description supplies the metric definition, the time window, the sibling alternative, and the exact response fields plus their time basis. Nothing an agent needs to call or interpret it correctly 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?

Only one parameter and schema description coverage is 100%, with the schema already explaining that the domain comes from list_sites or any public site. The description's 'Name the site by its domain' corroborates but adds no format or syntax detail beyond the schema, so the 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 metric with an exact operational definition: visitors with a pageview or other event in the last 5 minutes, matching the dashboard's live count. It explicitly contrasts itself with get_site_summary, so an agent can distinguish it from siblings without opening a schema.

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 both the scope ('now', 5-minute window) and a named alternative with the condition that selects it: 'for how many came over a day or more, use get_site_summary.' That is explicit when/when-not routing to a sibling.

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