Get Garmin fitness age

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

Annotations already establish this is a safe read-only, non-open-world call, so the bar is lower. The description still adds operational context beyond them: components may be marked stale when there is no recent data, and the VO2max exclusion prevents misreading the returned components. It does not say what happens when no fitness age exists for the date.

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?

It is a single, dense sentence that front-loads the resource and then enumerates what is returned, with a second short sentence for the stale-data caveat and a third for the VO2max clarification. Every clause carries information, though the embedded component list makes it slightly hard to scan.

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, so the description must convey the return shape, and it does so by naming the three age values plus the component breakdown and the stale flag. The only gap is the no-data/failure case for a given date, which the description leaves unstated.

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 single optional date parameter already documents the YYYY-MM-DD format and the 'today in user's time zone' default. The description only says 'on a date,' adding no semantics beyond the schema, so the baseline 3 applies.

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 names a specific resource (Garmin fitness age) and the exact payload: fitness age for a date, chronological age, achievable fitness age, and the underlying components (resting heart rate, BMI, vigorous days/minutes). It is clearly distinguishable from sibling metrics like garmin_get_hrv, garmin_get_body_battery, or garmin_get_profile, which share inputs but not outputs.

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?

It gives clear context for when this tool is the right one (querying fitness age for a given date) and explicitly rules out a common wrong assumption with 'Garmin does not use VO2max here.' It does not, however, name an alternative tool or state when not to call it (e.g., dates before a device supported the metric).

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