garmin_performance_metrics

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

No annotations are provided, so the description must carry the behavioral disclosure burden. It lists returned metrics but does not state that the operation is read-only, whether results vary by date, what 'where available' means in practice, or any other behavioral traits. The implied read-only nature is not explicitly stated.

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 a single, tightly packed sentence that front-loads the key content. There is no filler or repetitive information, and every word contributes to the tool's purpose.

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 simple one-parameter tool with a full output schema, the description conveys the essential metric categories. The vagueness of 'where available' is a minor gap, but the output schema and 100% parameter documentation cover most of what an agent needs.

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 schema fully documents the single date parameter with a default and format, so the description does not need to repeat it. The description adds no extra meaning about how the date affects the returned metrics, but 100% schema coverage keeps this at the baseline.

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 specific resources—VO2 max, lactate threshold, endurance/hill score, race predictions—making the tool's purpose clear and distinguishing it from siblings focused on sleep, heart rate, stress, etc. It lacks an explicit verb like 'retrieves' or 'returns', but the noun phrase is still informative and not a tautology.

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?

No guidance is given on when to choose this tool over related siblings such as garmin_training_status or garmin_recovery. The phrase 'where available' hints at data limitations but does not provide decision rules or alternatives.

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