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

Annotations already cover read-only, idempotent, non-destructive and closed-world behavior, so the bar is lower; the description nonetheless adds substantial context beyond them: live ephemeris computation at ~1′ accuracy, tropical zodiac on the true ecliptic of date, geocentric, UTC, and no interpretive layer. It also discloses the payment requirement ($0.01 USDC on Base via x402, HTTP 402 then retry with PAYMENT-SIGNATURE), which is exactly the kind of operational fact annotations cannot express.

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?

Content is front-loaded (payload contents first, then computation basis, then the payment mechanic) and nearly every clause carries information. It is dense and long, but the density is justified by the number of distinct facts being conveyed; no sentence is filler.

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?

With no output schema, the description carries the burden of explaining return values, and it does so thoroughly by enumerating each section of the response. The only gap is that response shape or size is not hinted at, which matters for a month-long payload an agent may need to budget context for.

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 the single 'month' parameter is fully documented with format and range in the schema itself. The description adds only the UTC framing and the breadth of output, not new semantics for the parameter, so the baseline 3 applies.

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 opening sentence names the concrete resource and enumerates exactly what the month payload contains: phases to the UTC minute, sign ingresses, void-of-course periods with last aspect, and per-day phase/illumination/lunar day/noon position. This is specific enough that an agent can distinguish it from moon_now (current status) and void_of_course without opening either schema.

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?

It routes the agent away from paid usage for simple needs by stating 'Free tools cover the current status and the next retrograde', which implicitly points to moon_now and the retrograde siblings. What it lacks is an explicit statement of when a whole-month calendar is warranted versus ephemeris_range, the closest sibling.

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