fitbit_get_cardio_fitness

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

With no annotations, the description fully discloses behavioral traits: it explains that VO2 Max is estimated from resting HR, HR during walks/runs, and demographics; it updates weekly; it caches and auto-syncs; and it returns a range (low and high). This is comprehensive.

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 concise and well-structured, starting with the core purpose, followed by behavioral context, then parameter details, and finally output explanation. 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 has 3 optional parameters and an output schema, the description covers inputs, behavior, and output interpretation (including the meaning of the range). It is fully complete for invoking the tool correctly.

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%, but the description thoroughly explains each parameter: start_date and end_date formats and defaults, and the live parameter for direct API fetch. It adds significant meaning beyond the schema titles.

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 retrieving a Cardio Fitness Score (VO2 Max estimate). It specifies the resource and differentiates it from sibling tools like fitbit_get_heart_rate or fitbit_get_activity by focusing on the VO2 Max estimate.

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 context on usage, noting the data updates roughly weekly and that by default it returns from cache with auto-syncing. It explains the parameters but does not explicitly state when not to use it or how it compares to alternatives.

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