get_custom_food_serving_units

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

Annotations already establish readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description usefully adds that a Garmin Connect+ subscription is required and names has_connect_plus as the way to verify it, but it states this requirement twice ('Requires ... subscription' and 'Needs Connect+') without adding anything on result shape beyond the bare '(13 units)'.

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 short, but the Connect+ requirement is repeated redundantly ('Requires a Garmin Connect+ subscription' / 'Needs Connect+'), and the front-loaded sentence is a prerequisite rather than the tool's purpose. The parenthetical '(13 units)' is left unexplained, costing a sentence's worth of clarity.

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 zero-parameter metadata fetch with annotations covering the read-only profile, the essentials (endpoint and subscription requirement) are present. It is still thin on why an agent would need the serving units and what each unit entry contains, and there is no output schema to compensate, so it lands at minimum-viable rather than complete.

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 and the schema is an empty object with additionalProperties=false, so there is nothing for the description to disambiguate. The baseline of 4 applies for a parameterless 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?

The description names the concrete endpoint (`/nutrition-service/metadata/customFoodServingUnits`) and hints at the result size (13 units), so the agent can infer it returns serving-unit metadata for custom foods. However, it largely restates what the tool name already conveys and gives no differentiation from the surrounding custom-food siblings (get_custom_foods, create_custom_food, update_custom_food), nor what the units are used for.

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 alternatives. The only usable signals are the Connect+ prerequisite and the pointer to has_connect_plus, which are environment/auth conditions rather than routing guidance about when this tool is the right choice.

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