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

The annotation readOnlyHint=true already signals basic safety, and the description adds far more behavioral context: it lists the returned data (phase name/label, day position, cycle, days until cross, tie) and confirms a compact summary string without editorial text. No contradiction with 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?

Two sentences, front-loaded purpose, then the complete returned field list, and then the target use case. No wasted words; every sentence earns its place.

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 read-only, read-only lightweight endpoint, the description gives enough to select and invoke it correctly: what is returned, what is not covered, and which consumer intents it fits. The schema fills the parameter details and annotations supply the safety profile.

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?

Because schema description coverage is 100 for all four paramameters — birthDate, targetDate, lang, compact — the schema carries the full parameter semantics. The description adds no parameter-specific guidance, but it isn't needed to be in the schema definition all already covers it.

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?

"Get current phase information for all 10 biorhythm cycles without the full interpretation payload" states the exact action and resource. It clearly differentiates from the reading-type siblings by emphasizing the lightweight, no-editorial-data nature. The title also separates it from dashboards and widgets.

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?

"Designed as lightweight endpoint for dashboards, widgets, status bars, and quick-access interfaces" offers clear consumption context, and the mention of the "full interpretation payload" implicitly routes users toward the heavier reading endpoint. It does not explicitly name sibling alternatives, but the context is clear.

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