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

Annotations already declare readOnly, idempotent and non-destructive, so the description's job is to add scope constraints — and it does, with the two-year maximum and the 60-day default window, neither of which appears in the annotations. It still omits error behavior on out-of-range input, which keeps it from a 5.

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 dense sentence front-loads the returned events, then attaches range and time-zone defaults as parentheticals. Every clause carries information, though the nested parentheses slightly hurt scanability.

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, return shape needs no explanation, and all four parameters are documented at 100% coverage. What remains thin is failure behavior and whether lang affects returned event labels rather than just the time format.

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 coverage is 100%, so the baseline is 3; the description earns a 4 by restating defaults in task terms (today + 60 days, Polish time) and by adding the two-year cap, a constraint that exists nowhere in the schema. Language selection and IANA time zone syntax are left entirely to the schema.

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 resource (new moons, first/last quarters, full moons) with precision ('to the minute') and range semantics, so an agent knows exactly what is returned. It does not explicitly contrast itself with the sibling moon_times, but the event-list framing is distinctive enough to infer the difference.

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?

Usage is implied by the defaults: from today for 60 days if dates are omitted, and a hard ceiling of two years. There is no explicit statement of when to prefer this over moon_times or sun_calendar, and no guidance on what happens if the range limit is exceeded.

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