Get all-day heart rate (one day)

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

Annotations already declare readOnly, idempotent, non-destructive behavior, so the safety profile is covered. The description adds useful context beyond that: it discloses the large payload size, explains the `heartRateValues` time-series shape and its `heartRateValueDescriptors` column mapping, which an agent cannot infer from structured fields alone.

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 what is returned, then the payload-size warning and alternative routing in the second sentence. The field enumeration is dense but each item earns its place; no filler sentences.

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?

With no output schema, the description carries the burden of describing returns and does so substantively (aggregate HR stats, alerts, time-series structure). Units (bpm) are only implied via the descriptor mention, a minor gap for a read-only single-parameter tool.

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 100% and the single `date` parameter is fully documented with format and timezone semantics in the schema. The description adds no input-side detail beyond what the schema already provides, so the 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?

States a specific verb (get), resource (heart rate), and scope (one day), then enumerates the exact fields returned. This clearly separates it from sibling tools like garmin_get_heart_rate_zones or garmin_get_hrv without requiring the agent to open any 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?

Explicitly routes the agent away from this tool for multi-day resting HR trends, naming garmin_get_daily_summaries as the alternative. It doesn't cover other plausible alternatives (e.g. heart rate zones) or when-not-to-use cases, but the key routing decision is stated.

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