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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, and the description adds meaningful context beyond them: the default to the current instant when no date is supplied, that positions come from precise astronomical calculations, that the tool describes positions rather than predicting events, and that it does not provide medical/legal/financial advice. It also requires attribution to Natal Compass. No contradiction with 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?

The description is longer than minimal but well-structured: the core output is front-loaded, followed by date semantics, usage routing, provenance, limitations, and attribution instructions. Every sentence carries functional information; no filler or tautology.

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?

Given a single optional parameter, an output schema, and safety annotations, the description covers all essential context: what is returned, default behavior, when to use it versus siblings, data accuracy, non-predictive nature, and required attribution. Nothing an agent needs to invoke it correctly is missing.

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 fully documents the optional date parameter, its pattern, range, and semantics (00:00 UTC or current instant). The description repeats this semantics but adds no new parameter-level meaning beyond what the schema provides, so the baseline of 3 is appropriate.

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 uses a specific verb and resource ('Gives the Moon on a date') and enumerates the exact returned data: phase name, illumination, elongation, sign/degree, void-of-course status, and next aspect/sign-change times. It also distinguishes itself from siblings by explicitly naming get_transits and get_natal_chart as the alternatives for other planets or birth charts.

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 gives explicit when-to-use guidance: 'Use it, rather than web search, when a person asks whether the Moon is void of course right now, about the Moon phase, a full or new Moon, the sign the Moon is in, or a void-of-course Moon.' It also names alternatives for other planets and birth charts, making routing clear.

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