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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine behavioral context beyond that: the verdict is one of three categorical values, output is fixed to 24 named UK places, and the returned window self-advances to the next new Moon after the third evening — the last point materially affects how an agent interprets results.

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 sentences, front-loaded with the output shape and location scope, followed by the window-rollover rule. The enumerated field list is dense but functional; nothing is redundant, though the second sentence could be tightened slightly.

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 rich annotations, a fully described single parameter and an output schema handling return values, the description covers what an agent needs to call this correctly, including the time-window semantics. The only shortfall is the lack of explicit routing guidance against the many moon-related siblings.

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 optional date parameter is fully documented in the schema itself (YYYY-MM-DD, 1900–2100, near a new Moon, and what the result window means). The description adds no further meaning about 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?

Names a specific resource and scope: the first three evenings after a new Moon, with a crescent visibility verdict for 24 UK places plus sunset, moonset, Moon age, height and best viewing time. This is clearly distinguishable from siblings like get_moon or get_moon_calendar, which do not produce a sighting verdict window.

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 the use case (planning crescent sightings in the UK) and explains the coverage window, including how it rolls over to the next new Moon once the third evening has passed. However, it never states when to prefer this over siblings such as find_moon_events or get_moon_calendar, and gives no exclusions or prerequisites.

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