User Session Count

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered without the description. The description adds the per-day aggregation grain, which is genuine behavioral context, but says nothing about pagination, empty-day behavior, or timezone effects. Adequate but not rich.

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, zero filler, and the core operation is front-loaded before the use-case example. 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?

An output schema exists, so return-value shape need not be explained. However, for a 7-parameter tool with an uncovered pastMinutes pair and timezone semantics, the description does not say how relative-minute ranges interact with startDate/endDate. It is enough to call the tool correctly for the common case, not for the full parameter space.

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 71%, so most parameters (siteId, userId, dates, timezone) are documented in the schema itself. The description adds only an implied time-range constraint ('across the requested time range') and gives no clarification of the ambiguous pastMinutesStart/pastMinutesEnd pair, which are the only undocumented parameters. Baseline 3 fits.

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: 'per-day session count for a single user across the requested time range.' The per-day granularity and single-user scoping make the operation concrete. It stops short of naming the nearest siblings (get_user_event_breakdown, get_user_traits) that an agent would otherwise have to differentiate by schema alone.

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 clause 'Useful for plotting user engagement intensity (calendar heatmap or sparkline)' gives one intended context, so usage is implied rather than explicit. There is no guidance on when to prefer this over get_user_event_breakdown, list_sessions, or get_retention, which is a real gap given the crowded user/session sibling set.

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