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 established. The description adds useful context about what values the tool computes and returns (phase name, illumination, lunar age, zodiac sign, distance), but it does not disclose potential edge cases, timezone effects, or how the optional parameters affect the result beyond what the schema already describes.

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 concise and front-loaded with the tool's core purpose and outputs. The phase-name enumeration is slightly verbose but useful because it disambiguates phase naming conventions. The final use-case sentence adds context but is arguably promotional rather than operational.

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?

There is no output schema, so the description carries the responsibility of explaining the return content; it does so by listing the computed fields and exact phase names. Given the simple read-only nature and the rich parameter schema, the description is sufficient for an agent to understand the tool's primary use, although it does not mention units for distance or detailed lunar-position naming.

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% and every parameter already has a descriptive explanation with defaults and examples. The description adds no parameter-specific guidance beyond naming the core result fields, so it does not meaningfully compensate beyond the schema, which makes the baseline of 3 appropriate.

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 identifies a specific verb ('Get'), a precise resource ('current moon phase'), and enumerates the returned data (illumination percentage, lunar age, zodiac sign, distance, phase name). The word 'current' distinguishes it from sibling tools that target future phases or yearly/monthly calendars, so an agent can clearly tell what this tool provides.

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 implies usage through phrasing like 'Get current moon phase' and 'Perfect for moon tracking apps, lunar calendars, astrology widgets, and gardening by moon phase tools.' However, it does not explicitly contrast this tool with its siblings, such as get_astrology_moon_phase_upcoming or get_astrology_moon_phase_calendar_year_month, nor does it state when not to use this tool.

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