fitbit_get_hrv

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

With no annotations, the description carries the full burden, disclosing default cache reads, the need for a prior sync, data sparsity, the Premium requirement, and the specific output fields. It also explains the meaning of RMSSD, adding interpretive context beyond a simple fetch.

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: a one-line summary, followed by cache behavior, caveats, parameter docs, and output explanation. Every section adds necessary value with no redundancy.

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 is comprehensive for a three-parameter tool, explaining the data source, prerequisites, limitations, and output format. Even with an output schema present, it clearly states the fields returned, and the sync instruction mitigates potential empty-cache confusion.

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 Args section provides detailed semantics for all three parameters, including accepted formats for start_date ('YYYY-MM-DD', 'YYYY-MM', or '30d'), defaults for start/end dates, and the boolean `live` flag. Since the schema has no property descriptions (0% coverage), this fully compensates.

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 opening line 'Get nightly HRV (heart rate variability) data' uses a specific verb and resource, clearly distinguishing it from sibling tools like fitbit_get_heart_rate and fitbit_get_sleep. The cache/live explanation further reinforces its unique role.

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 instructs to 'Run fitbit_sync first to populate the cache' and offers the alternative of 'Use live=True to fetch from Fitbit API', giving clear when-to-use and prerequisite guidance. It also notes the Premium requirement, which helps the agent decide applicability.

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