get_hrv

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: values are in milliseconds, missing Garmin data is returned as 'not recorded' rather than zero, and results are informational not medical. It does not discuss rate limits or data latency.

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 compact sentences, front-loaded with the resource and scope, then the unit, then the interpretation caveats. The leading 'T3.' token is unexplained noise, but no sentence is redundant.

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 shape needn't be explained; the description instead supplies the two things an agent would otherwise get wrong — units and the 'not recorded' sentinel. Combined with full schema coverage and a complete annotation set, an agent has what it needs to call this correctly.

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 100%, including the 90-day maximum span on 'end', so the schema carries the parameter burden and baseline 3 applies. The description confirms the date-range framing and adds units for the returned values but contributes nothing about the start/end semantics that isn't already structured.

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) and a specific resource (heart rate variability per night over a date range) and enumerates the returned measures (last-night average, weekly average, 5-minute high, status, personal baseline) in milliseconds. This is clearly distinguishable from siblings like get_heart_rate or get_sleep by resource. It stops short of explicitly naming a sibling to disambiguate against.

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 is implied by the resource and the date-range constraint, but there is no explicit when-to-use/when-not guidance relative to get_heart_rate, get_sleep, or get_daily_overview. The one instruction given ('never treat not recorded as zero') is about interpreting output, not about selecting the tool.

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