Heart rate variability

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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds context about the temporal scope ('one day'), the specific data included (weekly vs last night averages, baseline range, status), and the typical use case. It does not mention any side-effect or hazardous behavior, which is appropriate for a read-only operation.

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?

The description is two sentences long, with the first sentence delivering the core functionality and outputs, and the second sentence providing usage context. Every word earns its place; there is no redundancy or filler, making it highly efficient.

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?

Given the tool's moderate complexity, the description covers the key aspects: what it returns, the one-day scope, and when to prefer it. The schema handles parameter details, and no output schema exists, so the description adequately informs the agent about expected behavior. It could mention the return format, but that is not critical for selection.

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?

The input schema provides 100% coverage with clear descriptions for both 'date' and 'detail', including relative date syntax and the warning that 'full' can be 'potentially enormous'. The description does not need to add further parameter details since the schema is already comprehensive, and it adds no extra parameter-specific nuance beyond what is documented.

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 clearly states the tool retrieves 'overnight heart rate variability for one day' and enumerates specific outputs (weekly average, last night's average, baseline range, HRV status). It uses a specific verb 'Get' and a distinct resource, making it easy to understand its function and differentiate from sibling tools.

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?

The description explicitly advises to 'prefer this when asked about recovery trends rather than a single night's sleep,' which contrasts with the sleep tool. It also provides rationale ('HRV is the most sensitive single indicator of accumulated stress or illness'), giving clear guidance on when to use it over alternatives.

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