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

Annotations already declare readOnly, idempotent and closed-world behavior, so the bar is low. The description adds real value beyond them: all times are in UTC and the two-year-per-call cap is a hard operational limit not visible in annotations.

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 tight sentences with zero waste: the event set is front-loaded and the hard limit follows immediately. Nothing needs trimming.

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 three params, no output schema, and annotations covering safety, the description supplies what an agent needs: the event categories, the time basis (UTC), and the range limit. Only the exact shape of returned entries is left unstated, which is a minor 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 coverage is only 33% – only kinds carries a description ('Default all three'). The description compensates partially by establishing that from/to are the range endpoints and that results are exact UTC moments, and it restates the kinds default, but adds no format detail beyond the schema's date regex.

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 precise verb-set and resource: planets changing sign, lunations (new/full/quarters), and stations within a date range, each with an exact UTC moment. An agent can distinguish this from eclipses, transits, or sky_now without opening the 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?

Phrases like 'Between two dates' and 'At most two years per call' imply when the tool applies and its scope constraint, but no alternative is named and no exclusion is given (e.g., use eclipses for eclipse events). Usage is implied rather than explicit.

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