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

Annotations only declare it as a non-read-only, non-destructive, open-world write. The description adds substantial behavior beyond that: merge rather than replace semantics, the non-empty `settings` validation rule with the specific `GarminError`, and the multi-step GET-overlay-PUT flow including `id` resolution.

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 with the core action and merge semantics, then the precondition, then validation and flow details. Dense but every clause carries information; the endpoint path detail is slightly more implementation-level than an agent needs.

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 nested-object mutation with no output schema and no schema descriptions, the description covers merge behavior, precondition, error case, and underlying request flow. It does not enumerate which setting keys are accepted, though `additionalProperties: true` makes that open-ended.

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 coverage is 0%, so the description must compensate, and it largely does: it defines `settings` as a non-empty object overlaid onto the current `userMenstrualCycleSettings`, and hints at the `id`/`userSettingsId` role via 'including `id` if resolvable'. The `options` object itself is never named or explained.

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 and resource ('Changes cycle-tracking preferences') with the added qualifier that changes are merged into existing settings. It does not name or contrast with close siblings such as init_menstrual_cycle_setup or update_menstrual_daily_log, so differentiation is left to the agent.

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?

'Has no effect until cycle tracking is set up in Garmin Connect' gives a clear precondition that implicitly routes the agent to init_menstrual_cycle_setup first. No explicit when-not or named alternative is given, but the operative context is present.

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