Daily totals over a date range

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real behavioral context beyond them: hard range caps that differ by data type (14 days for heart-rate, active-minutes, total-calories, calories-in-heart-rate-zone; 90 days otherwise), which is not present in the schema and directly affects call planning. It does not say what happens when the cap is exceeded (error vs truncation), which keeps it from a 5.

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 tight sentences, front-loaded with what is returned and the bucketing model before the constraint sentence. No filler. The date-limit sentence is dense but every clause carries a distinct, actionable constraint.

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 4-parameter read tool with no output schema and presence/absence of annotations covering only safety, the description supplies the essentials: bucketing semantics, examples of the per-day vs per-N-days output, and range limits. Remaining gaps are boundary behavior (does an out-of-range request error or clamp?) and timezone handling of startDate/endDate across buckets.

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 coverage is 75%, so dataType, startDate, endDate and windowDays are all documented in the schema, including the default-1 and 7-for-weekly behavior of windowDays. The description reinforces this with the "per N days" and "weekly distance" phrasing but adds no new semantics such as unit of the returned values or how partial buckets are handled at range boundaries. Baseline 3 is appropriate.

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 states a concrete verb+resource: aggregated values bucketed per day (or per N days) for a named data type, with three illustrative examples (steps per day, average heart rate per day, weekly distance). It establishes its role as the trends tool, but never names or contrasts the near-identical siblings get_rollup and get_daily_summary, so an agent cannot fully disambiguate from the text 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?

"Best tool for trends" is a usable when-to-use cue, and the per-data-type max range (14 vs 90 days) tells the agent when the call will fail. However, no alternative is named for point-in-time retrieval, and the relationship to get_daily_summary/get_rollup is left implicit, which is a significant gap given how similar those siblings appear.

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