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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, and the description is consistent with all of them. It adds real context beyond the annotations: all times are UK time GMT/BST, dates are constrained 1900–2100, and place is restricted to 24 UK locations. It does not discuss error behavior for out-of-range places or dates.

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?

Only two sentences, but the first is an extremely dense run-on enumerating every returned field, which duplicates the output schema and makes it hard to scan. It is front-loaded with the purpose, yet trimming the field list would improve readability without losing agent-relevant information.

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 an output schema present, the description need not enumerate return values, and it correctly covers the input-mode semantics, time zone, place restriction, and date range. An agent has everything needed to call it correctly; only the absence of routing guidance to sibling tools is a gap.

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%, so the schema already documents each parameter's format, pattern, and defaults. The description's opening sentence usefully consolidates how the three parameters combine into different snapshot modes, but adds no format or constraint detail beyond what the schema states.

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 a specific verb ('Returns') and enumerates concrete resources: phase, percent lit, lunar age, distance, waxing/waning, full/new Moon timing, and location-specific moonrise/transit/moonset. This clearly separates it from siblings like get_moon_calendar or get_moon_sign, though it never names an alternative explicitly and partially restates what the output schema already declares.

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 spells out the three invocation modes clearly: no date/time gives the Moon right now, a date alone gives 12:00 UK time, and date+time gives that clock time; adding a place unlocks rise/set/visibility. There are no explicit exclusions or named alternatives, so an agent must infer when to prefer find_moon_events or get_moon_calendar.

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