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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower; the description still adds real context by disclosing the 'now' default and that place-dependent fields only appear when a place is given. It omits failure modes (invalid or ambiguous place names have no stated behavior) and pagination/precision caveats.

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?

Dense but front-loaded: the output inventory comes first, the place-conditional second, and the routing examples last. Every clause carries information and there is no filler.

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 and rich annotations already present, the description covers what is needed: returned fields, the default time, and the place-dependent extras. Remaining gaps are precedence between place and lat/lon and what happens on an unmatched place name.

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 baseline is 3, but the description adds meaning beyond it: date omission implies the current moment, and place is explained as a mode switch that adds angles and houses rather than just another coordinate input. It does not clarify how place interacts with or overrides lat/lon when both are supplied.

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?

Specific verb-and-resource: reports zodiac positions (signs and degrees), retrogrades, aspects, Moon phase and next sign change, and lunations at a moment. The phrase 'at a moment' and the sample questions ('what sign is the Moon in today') implicitly separate it from the natal-chart sibling birth_chart and from astro_calendar/sign_dates, so an agent can pick it without opening a 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?

Gives concrete triggering questions and the key rule that omitting the date means 'now', plus the conditional that supplying a place switches on ascendant/midheaven/houses. It stops short of stating when NOT to use it or naming an alternative sibling (e.g. for natal charts or calendar lookups).

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