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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds genuinely useful scope boundaries (wellbeing only, not medical/contraception use), though it says nothing about return shape beyond the topic areas.

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?

Two tightly packed sentences with the usage guidance front-loaded after a short purpose statement. The main waste is that the first sentence duplicates the title verbatim rather than adding 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?

For a zero-parameter, no-output-schema reference tool, the description covers purpose, routing conditions, and scope exclusions adequately. It could be more complete by noting that all phases are returned at once, but nothing essential is missing.

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?

The tool takes zero parameters and the schema confirms an empty object, so the baseline is 4. The description correctly offers no parameter detail because none exists.

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 first sentence states the resource (cycle phases) and the content returned: what each phase feels like plus workout and food ideas. It is clear enough to distinguish from the dated siblings, though it never literally says 'list all phases' or names those siblings.

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?

Strong when-to-use guidance: 'For general questions about cycle syncing that need no dates' with a concrete example query, plus an explicit when-not list (conception, fertile days, contraception, pregnancy). It stops short of naming the sibling tools for date-based queries, leaving that routing to inference.

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