add_body_composition

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

Annotations already declare readOnly=false, destructive=false, and openWorld=true, so the safety profile is set. The description adds meaningful behavioral detail: weight is validated positive/finite with a thrown GarminError, and the upload result is passed through unchecked. It does not cover auth, rate limits, or side effects beyond the upload.

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?

A single dense sentence front-loads low-value implementation trivia (file path `src/util/fit.ts`, internal endpoint `/upload-service/upload`) instead of purpose or usage. These internals do not help an agent select or invoke the tool, so they do not earn their place.

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 mutation tool with a 12-field nested object and no output schema, the description is incomplete: it omits any explanation of the optional body-composition metrics. It covers the upload path but leaves an agent without the information needed to populate `extra` correctly.

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% and the bulk of parameters live in a nested `extra` object with 12 undocumented fields (bmi, muscleMass, percentFat, etc.). The description only clarifies validation on `weight` and says nothing about what the `extra` metrics are or how they map, so it fails to compensate for the coverage gap.

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 describes the mechanism (builds a `.fit` binary and uploads it) rather than the user-facing outcome of adding body-composition data. An agent can infer the purpose from the tool name, but the text itself never states 'adds body composition/weight data' explicitly and gives no differentiation from siblings like add_weigh_in or add_weigh_in_with_timestamps.

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 when-to-use guidance, no prerequisites, and no mention of the many closely related siblings that also write body data. The description only covers implementation flow, leaving the agent to guess when this tool is preferred over add_weigh_in.

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