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

Annotations only cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true). The description adds substantive behavior beyond them: the Connect+ auth gate, the non-obvious PUT-vs-POST transport quirk, that numbers are serialized as strings, that values are absolute (not %DV), and what the call returns (foodId/servingId).

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?

Front-loads the hard prerequisite, then the field contract, then the return value – a sensible order. Minor waste: "Needs Connect+" repeats the opening subscription requirement, and the raw endpoint path is borderline verbose, but overall it packs high-value detail without padding.

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 tool with a 19-field nested input, no output schema, and no per-field schema descriptions, the description supplies the shape, defaults, per-serving/absolute-value semantics, serialization quirk, and return contract. Units per nutrient are the only thing an agent might still need, but the essentials for correct invocation are present.

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%, so the description must carry the load, and it does: it enumerates the CustomFoodInput fields with defaults (servingUnit="G", servingSize=100), and clarifies the critical semantics that values are per ONE serving and absolute rather than %DV. It stops short of stating the expected unit per nutrient (mg vs g), which is the remaining gap for a 19-field nested object.

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?

States a specific verb+resource ("Creates a custom food") and adds the scoping detail "per serving." It also names related siblings implicitly (has_connect_plus for the prerequisite, logFood for the returned IDs), so an agent can place it in the nutrition workflow without opening a schema.

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?

Gives a concrete prerequisite and how to verify it: "Requires a Garmin Connect+ subscription (check with has_connect_plus)." It also explains where the returned IDs go (logFood). It does not, however, name the modify path (update_custom_food) or when to prefer quick_add_food/search_foods, so an explicit alternative/exclusion statement is missing.

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