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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the algorithmic basis (Meeus Ch.48, geocentric) and the 10-credit consumption cost. It still says nothing about geographic sensitivity, caching, or rate limits, so it adds moderate rather than rich 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?

Two tight sentences with the computed outputs front-loaded, followed by a compact methodology note and bracketed metadata. No filler or redundancy, though the group/cost tags are appended rather than integrated.

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?

An output schema exists, so return values need no explanation, and the description correctly focuses on what is computed. However, with 15 parameters at 33% schema coverage and no usage guidance, the definition is incomplete for an agent trying to assemble a correct call — particularly around whether location is truly needed for a phase value.

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 only 33% across 15 parameters, so the description must carry more of the burden and does not. It never mentions the four required inputs (date, time, latitude, longitude), the timezone vs timezoneOffset interaction, ayanamsa/zodiacType choices, or the compact-mode fields/precision options.

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 names the specific resource and enumerates exactly what is computed: illumination %, age in days, elongation, waxing/waning, and sun/moon zodiac signs, plus the method (Meeus Ch.48 geocentric Sun-Moon elongation). An agent knows precisely what this produces. It does not, however, distinguish itself from closely named siblings such as astroway_render_moon_phase or astroway_calendar_lunar_calendar.

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?

There is no when-to-use guidance, no statement of prerequisites (e.g. that latitude/longitude and a local date/time are mandatory), and no routing to alternatives like the moon-phase renderer or the lunar calendar. The bracketed group/cost tags are metadata, not usage guidance.

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