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

The description discloses what the operation does beyond the readOnlyHint: it overlays cycle profiles on a target date and returns computed alignment scores, an overall score, rating, and detailed narrative outputs. It also flags that compatibility is date-dependent. There is no contradiction with annotations, and no hidden mutation is implied.

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: the first sentence states what the tool does and the target input, the second sentence lists key outputs, and the third sentence gives actionable use cases. Every sentence contributes context without redundancy.

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 though there is no output schema, the description enumerates the important return fields: per-cycle scores, overall score, relationship rating, strengths/challenges, advice, and daily sync snapshot. Combined with the schema's detailed parameter documentation, an agent has enough guidance to invoke the tool and interpret its result.

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 input schema has descriptions for targetDate, lang, compact, and birthDate nested under person1 and person2, but schema description coverage is only 60%. The description adds little parameter-specific detail beyond mentioning the target date. It does not explain compact mode, language behavior, or person-object shape, so it doesn't significantly compensate for the coverage gap.

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 starts with a specific verb and resource: 'Calculate biorhythm compatibility between two people by overlaying their cycle profiles.' This clearly distinguishes it from the sibling biorhythm tools, which are single-person daily, forecast, phases, or critical-day calculations. It also specifies the main output categories, so an agent can recognize the intended operation quickly.

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 use contexts such as dating apps, relationship platforms, team-building tools, and couples coaching. It does not explicitly list alternative sibling tools or exclusion criteria, but the 'between two people' phrase and the compatibility focus make the intended scenario evident. A small gap is that it never says 'use a single-person biorhythm tool if there is only one person.'

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