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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so safety is covered. The description goes beyond that by disclosing the construction of a .fit binary in memory, the upload endpoint, and the validation/error contract ('weight validated positive/finite, throws GarminError otherwise') – genuinely useful behavioral context an agent couldn't infer from annotations.

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-loaded and information-dense, but the second sentence repeats the .fit-in-memory point already made in the first ('uploaded as a `.fit` weight-scale file built in memory' vs 'Builds a `.fit` binary in memory'), spending words on redundancy rather than the missing field documentation.

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 no-output-schema mutation tool with a nested 12-field object at 0% schema coverage, the definition covers the write mechanism and validation but leaves the bulk of the body-composition fields and the return behavior unspecified. Partially adequate but with real gaps.

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 carries the full burden. It clarifies that weight is in kilograms and must be positive/finite, but the nested 'extra' object has 12 subfields (bmi, basalMet, boneMass, muscleMass, percentFat, etc.) and the description names only two examples ('body fat and muscle mass'). Most parameters remain undocumented in both schema and description.

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 states a specific verb and resource ('Records a weight (kg) with optional body-composition fields') and adds the transport mechanism (.fit weight-scale file). However, it never differentiates itself from the very close siblings add_weigh_in and add_weigh_in_with_timestamps, so an agent can't tell from the description alone which weight-writing tool to pick.

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 or when-not-to-use guidance. With three near-identical weight-writing siblings (add_weigh_in, add_weigh_in_with_timestamps, add_body_composition), the description should route the agent but instead offers only an implied purpose.

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