Fitbit Heart Series

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

Annotations already declare readOnly, openWorld, and idempotent hints. The description supplements with behavioral specifics: bounded series, 500-point cap, agent-safe-series/v1 contract, and a 'Not medical advice' disclaimer. It does not contradict annotations; slight deduction for not disclosing potential response-size limits beyond the cap, though the cap itself is useful.

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 three sentences, with each sentence adding meaningful information: the core capability, guidance on alternatives, and the shared contract plus disclaimer. It is front-loaded with the primary purpose and contains no filler.

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?

For a read-only series tool with an output schema, the description covers the primary purpose, the 500-point cap, preference ordering, and cross-platform compatibility. It could mention response formatting or the exact output type, but the output schema exists and fills those gaps. Overall quite 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 88%, so the baseline is 3. The description reinforces that the series is downsampled and capped at 500 points, which relates to max_points and resolution_seconds, but it does not add per-parameter semantics that the schema already provides. Since the schema handles parameter documentation, a 3 is appropriate.

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 identifies the tool as a bounded heart-rate time-series for a civil day, with exact stats on full-resolution samples and a downsampled series capped at 500 points. It distinguishes itself from fitbit_get_heart_day by emphasizing the 'shape of HR over the day' and references a shared series contract.

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?

Explicitly instructs to prefer fitbit_get_heart_day or daily summary first, and to use this tool only when the shape of HR over the day is needed. Naming concrete alternatives and providing a clear when-to-use condition fully satisfies this dimension.

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