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

Annotations already declare readOnly=true, idempotent=true, destructive=false, openWorld=false, so safety is covered. The description adds genuinely useful non-annotation context: the 100-credit Tier 4 cost, which lets an agent weigh whether the call is worth it. Return-format detail is light but the output schema exists, so this is the right area to add value.

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?

A single front-loaded sentence with zero filler, followed by compact bracketed metadata for group and cost. Every element 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, two-required-param aggregation tool with an output schema, the definition covers purpose, contents, and cost adequately. The only real gap is the absence of any usage/routing guidance, which is minor given the tool's simplicity.

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 50%: the non-obvious params (fields, precision) are documented in the schema, while year/month are self-explanatory from their names. The description adds nothing beyond "given month" — no format hints, ranges, or defaults — so it neither compensates nor detracts.

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?

States a specific verb ("Calculate") and resource ("a lunar calendar for a given month"), then enumerates the outputs (Moon sign per day, lunar phases, VOC windows, perigee/apogee). The enumeration implicitly distinguishes it from the single-purpose siblings astroway_calendar_moon_phase and astroway_calendar_moon_voc, though no sibling is named explicitly.

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 only says "for a given month" — there is no when-to-use vs. when-not guidance and no routing to alternatives like the individual moon-phase or VOC tools. An agent must infer the aggregation-vs-single-purpose distinction entirely on its own.

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