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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description goes beyond annotations by explaining the zero-crossing detection behavior, the severity categories, and the special highlighting of double and triple critical days, which is genuinely useful behavioral context.

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?

The description is compact and front-loaded, stating the core operation in the first sentence. The second and third sentences add valuable output and use-case context without wasted wording, though the final use-case list could be trimmed without losing essential meaning.

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?

Even without an output schema, the description lists the key return fields: critical day, cycle name, period, direction, severity, and advisory text. Parameters are fully covered by the schema, and the date-range limit is stated. Together this is enough for correct call construction and reasonable response expectations.

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 100%, so the schema already documents all five parameters, including formats, defaults, and language enum. The description adds context about the 180-day range and the nature of critical days, but it does not add significant meaning beyond the schema.

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 opens with a precise operation, 'Find all critical days (zero crossings) within a date range up to 180 days,' which names the resource, action, and scope. It also lists the returned information, including severity and direction, making it easy to distinguish from the sibling biorhythm tools.

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?

The description gives clear context for when the tool is appropriate: date-range searches for critical days, up to 180 days. It also names ideal use cases like calendar integrations, push notifications, alert engines, and wellness scheduling. It does not explicitly exclude alternatives or name a sibling to use instead, but the context is strong enough for agent selection.

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