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

Annotations already flag destructiveHint=true and readOnlyHint=false, but the description goes well beyond them: it discloses that the operation is a full replace rather than a merge, that there is no undo, the input validation rules that trigger a GarminError, and a required user-confirmation step.

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?

Four dense sentences, no filler, with the core mutation semantics ('full replace') front-loaded ahead of the preconditions and validation rules. Every sentence carries actionable information.

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?

Covers the mutation semantics, irreversibility, prerequisites, and failure mode for a nested-object, no-output-schema tool. Minor gaps remain: the purpose of options.todayCalendarDate and the shape of a successful response are unstated.

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 only 50%, but the description compensates by explaining cycleDatesLists semantics in depth: each group must be non-empty, be consecutive calendar dates, and fall within [startdate, enddate]. It adds little about startdate/enddate or options.todayCalendarDate, which keeps it from a 5.

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 precise verb and resource: 'Rewrites the period days in a date range.' The scoping to a date range plus the emphasis on 'full replace, not a merge' makes it clearly distinct from sibling mutators like update_menstrual_daily_log or confirm_menstrual_period_start.

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 hard precondition ('Needs cycle tracking set up in Garmin Connect first') and an explicit call-time instruction ('IRREVERSIBLE: confirm with the user before calling'). It does not name alternative tools for the other menstrual-editing cases, so it stops short of a 5.

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