Intraday health data

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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds substantive behavior on top: on-demand remote fetching for days older than 150, degraded data availability because Garmin retains intraday HR/HRV for only ~4-5 months, and the fallback that ancient days may return only the day summary. Device prerequisites for HRV and SpO2 are also surfaced.

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?

Purpose and metric list are front-loaded in the first sentence, then return shape, then availability caveats, then defaults — a logical order. It is dense but nearly every clause carries operational information; the defaults sentence slightly duplicates schema defaults.

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 return-value burden itself and does so precisely: per-metric min/avg/max, day summary values such as resting HR and Body Battery charged/drained, and a columnar series of local HH:MM timestamps plus values. Together with the retention caveats, an agent knows both what it will get and how complete it will be.

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 the baseline is 3, and the description earns an increment by giving units and ranges for each metric value (bpm, Body Battery 0-100, HRV in ms, SpO2 in %) plus restating the effective defaults for date, metrics and interval. Only response_format is left entirely to the schema, so it stops short of a 5.

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 first sentence gives a specific verb (get), resource (one day's health data) and a clear differentiator (averaged into intervals, listing the four metrics). The intraday/interval framing implicitly separates it from summary-style siblings like garmin_get_daily_health and garmin_get_hrv, but no sibling is named, so the agent must infer the boundary.

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?

Usage context is unusually clear: it states defaults (today, all four metrics, 15-minute intervals), that the last 150 days are pre-synced while older days trigger an on-demand Garmin fetch, and that HRV/SpO2 require a compatible watch with pulse ox enabled. What's missing is explicit routing — it never says when to prefer garmin_get_daily_health or garmin_get_hrv instead.

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