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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description instead adds genuinely non-obvious behaviour — twelve event pairs per star-planet combination, exactness because it is solved on hour angles rather than quantised to a polyline step, and the row contents (which body does what, latitude, meridian). It does not mention credit cost or rate behaviour, but those appear in the endpoint context.

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 core definition is front-loaded and every sentence carries information, but the prose is dense and jargon-laden in places ('minus meridian against meridian', 'equator mirror') and could be tightened without loss. It is appropriately sized for a conceptually unusual tool.

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 values need not be enumerated, and the description still sketches the row shape. Combined with annotations covering safety and a fully described input schema, an agent has enough to call the tool correctly; only the sibling-routing condition 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%, including rich text on timezone, ayanamsa, and the star/planet/horizon/latitudeLimit sub-fields, so the schema already does the heavy lifting. The tool description itself adds only the note that birth coordinates are unused for parans, which duplicates the body-schema text rather than extending it.

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 opening clause states precisely what is computed — 'Latitudes where a fixed star and a planet are angular at the same moment' — and immediately clarifies the output class ('not a place, a latitude'), which separates it from the ACG/polyline map tools in the sibling set. It also pre-empts a likely confusion by noting that 'minus meridian against meridian' is a shared right ascension, not a paran.

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 rather than routed: an agent can infer this is the tool for star-planet paran latitudes, and the contrast with polyline intersection hints at when not to use map-based tools. However, it never names the obvious alternative (astroway_geo_parans) or states the conditions that select between them, so the agent must infer the boundary.

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