Fitbit Daily HRV

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

Annotations (readOnlyHint=true, idempotentHint=true) already indicate safe, idempotent behavior. The description adds context about availability constraints (device/data) and non-medical nature, which supplements annotations without contradiction. It does not detail error handling, but overall transparent.

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 with no unnecessary words. It front-loads the core purpose and includes essential prerequisites and caveats. Every sentence adds value.

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 simplicity, the description covers prerequisites, limitations, and domain context. An output schema exists, so return values need not be described. No gaps evident.

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 67% with three well-described parameters (date, privacy_mode, response_format). The description adds no extra parameter guidance beyond schema. Since schema already provides good descriptions and enums, baseline score 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?

The description clearly states the tool's function: 'Get HRV summary for a date when available.' It uses a specific verb ('Get') and resource ('HRV summary'), and distinguishes from sibling tools (e.g., fitbit_get_heart_day) by focusing on HRV. It also mentions prerequisites and caveats, providing clear purpose.

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 provides usage context: 'when available', 'Requires heartrate scope and supported device/data', and the caveat 'Not medical advice'. It does not explicitly state when not to use or suggest alternatives, but given sibling tools for other metrics, the intended use is clear.

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