Fitbit Daily SpO2

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is clear. The description adds value by disclosing the required auth scope ('heartrate scope') and a disclaimer about medical advice, which provides context beyond annotations. It does not elaborate on error handling or output details, which is acceptable given the annotations.

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 exceptionally concise: three sentences that front-load the core action ('Get SpO2 summary for a date when available'), state a prerequisite, and add a necessary disclaimer. There is no wasted text, and every sentence earns its place.

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 (3 optional parameters, output schema present, rich annotations), the description covers the essential functional, behavioral, and prerequisite information. It does not explain what happens when data is unavailable or detail the return structure, but those gaps are partially filled by the schema and annotations.

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 already describes two out of three parameters (date and privacy_mode) with sufficient detail, achieving 67% schema description coverage. The tool description does not add additional meaning beyond what is already in the schema, so a baseline score of 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 states it retrieves a SpO2 summary for a specific date, using the verb 'Get' and specifying the resource. It mentions data availability ('when available'), which adds clarity. However, it does not explicitly distinguish this tool from sibling tools like fitbit_get_heart_day, making it a 4 rather than a 5.

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 minimal usage guidance: it notes the required scope ('Requires heartrate scope') and a disclaimer ('Not medical advice'), but it does not specify when to use this tool versus alternatives, nor does it mention prerequisites or caveats like checking data availability first.

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