Fitness age

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds real behavioral context: per-component stale flags, BMI sourced from the last weight entry and therefore 'often old', and an instruction to round the decimal. It does not discuss data availability or failure modes when no fitness age exists.

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?

Front-loaded with the core resource and its fields, then caveats. The middle sentence listing components is long and run-on, and the numOfWeeksForIm field name is opaque, but overall little waste.

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?

There is no output schema and only one parameter, so the description must carry the return-value burden — and it does, naming every field, its units, its staleness signal, and how to format the fitnessAge value. Nothing essential for a correct call is missing.

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 coverage is 100% and the enum/pattern are already documented, so the baseline is 3. The description adds practical meaning by explaining why 'today' is normally the right value, which the schema alone does not convey.

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?

States a specific resource ('Garmin's fitness age as of a date') and enumerates the exact payload fields (chronologicalAge, fitnessAge, previousFitnessAge, components). It also preempts the most likely confusion by declaring 'This is not VO2 max', which separates it from nearby wellness siblings.

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?

Gives concrete guidance that date='today' is usually sufficient because the metric changes slowly, which steers the agent away from over-querying history. It stops short of naming an alternative tool or stating when not to call it, but no sibling clearly overlaps.

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