get_fitness_age

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

With no annotations, the description carries the full burden, and it does disclose one real behavioral trait: the tool only works against the personal API (an auth/access constraint an agent needs). It says nothing about whether data must be synced first or whether a missing value is possible.

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?

Two short sentences with the resource front-loaded and the access constraint appended; nothing is padded. The phrase 'Personal API only' is terse to the point of being slightly opaque.

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?

An output schema exists, so return values need not be described, and no parameters need explaining. What remains missing is the sibling relationship to get_fitness and any hint about data freshness, which matters for a 'today' scoped metric.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; the schema is trivially complete. Baseline 4 applies for a no-argument tool.

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?

Names a specific resource (Garmin's fitness age) and scopes it temporally to 'today', so the agent knows exactly what is returned. It does not distinguish itself from the nearby get_fitness sibling, leaving the boundary between generic fitness metrics and fitness age implicit.

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?

There is no guidance on when to call this versus get_fitness or get_training_load, and no stated preconditions such as needing a recent activity sync. 'Personal API only' is an access constraint, not a usage rule.

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