Get heart rate variability (one night)

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

Annotations already declare read-only, idempotent, non-destructive behavior, so the description's contribution is the prerequisite that a compatible watch must be worn overnight, plus disclosure of the returned data shape. That is meaningful context beyond what the annotations provide, though error behavior when no HRV is recorded is not covered.

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?

One front-loaded sentence naming the resource and date scope, followed by the return-field enumeration and prerequisite. Dense but largely earning its place; the long parenthetical status list is somewhat bulky.

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 takes on the burden of describing returns and does so concretely: hrvSummary fields, status enumerations, hrvReadings in ms, and sleep window timestamps. Only the no-data/error case is unaddressed.

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 parameter's date semantics ('morning after the night measured') are fully documented in the schema itself. The description adds only 'for one date' and no format or edge-case detail beyond the structured field, so the baseline 3 applies.

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 ('Get overnight HRV') with a clear scope ('one date'), which implicitly differentiates it from the plural sibling garmin_get_hrv_summaries. An agent can tell what this returns without opening the 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?

Usage is implied by 'for one date' and the overnight-watch prerequisite, but there is no explicit when-to-use guidance and no named alternative such as garmin_get_hrv_summaries for multi-night data. The agent must infer the routing.

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