fitbit_get_hrv

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

With no annotations provided, the description fully discloses behavior: returns cached data by default, fetches from API with live=True, explains sparsity (only nights with on-wrist sleep tracking), and the Premium requirement. It also describes output fields and their interpretation.

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 well-structured with a clear first line, paragraphs for caching and restrictions, then Args, then Returns. Every sentence adds value without unnecessary words.

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?

The description covers purpose, parameters, behavior, output fields, and prerequisites. It lacks details on error conditions, rate limits, or authentication beyond Premium requirement. However, given the presence of an output schema and low parameter count, it is largely complete.

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 0%, so the description compensates with a dedicated 'Args' section that explains each parameter's format, default values, and purpose (e.g., start_date accepts 'YYYY-MM-DD', 'YYYY-MM', or '30d' with default last 30 days). This adds significant meaning beyond the schema's type-only definitions.

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 starts with 'Get nightly HRV (heart rate variability) data,' clearly stating the verb (get) and resource (nightly HRV data). It distinguishes from sibling tools like fitbit_get_heart_rate and fitbit_get_sleep by specifying HRV.

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 clear usage context: it mentions the default cache behavior, the live parameter for direct API calls, the prerequisite to run fitbit_sync, and the requirement of Fitbit Premium. It does not explicitly state when not to use this tool, but the context is sufficient for decision-making.

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