get_fitness_age

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description contributes the useful detail that the response includes the driving factors, not just a number, but says nothing about how the value is computed, how current the 'latest' result is, or what happens when no date is supplied.

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?

One sentence, front-loaded with the verb and resource, with the extra clause about driving factors earning its place by telling the agent what comes back. No padding or redundancy.

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, single-parameter read tool with annotations and no output schema, the definition covers the essentials. The gaps are the default behavior when the nullable date is omitted and the expected date format, both of which an agent needs in order to call it confidently.

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% for the single optional, nullable 'date' parameter, so the description must carry the meaning. 'As of a date' does clarify that the parameter selects the point in time for the measurement, but it never states the accepted format or that omitting it returns the most recent value.

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 verb and resource ('Get the latest Fitness Age') and adds the return content ('the factors that drive it'), which makes it distinct from the sibling metric tools such as get_steps or get_sleep. It stops short of explicitly differentiating itself from those siblings, but the resource is unique enough that confusion is unlikely.

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 explicit when-to-use guidance, no mention of prerequisites, and no reference to an alternative tool. The phrase 'as of a date' weakly implies you can retrieve historical values, but nothing states whether to omit the date for the current value or how this differs from get_daily_summary-style tools.

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