Planet positions at a time

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description adds real context beyond them: the supported date window, the tropical frame, 'apparent geocentric' ephemeris basis, and a stated accuracy provenance (checked against NASA JPL Horizons). It does not say what happens for a date outside 1800–2200 or what the response envelope looks like, which keeps it short of 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?

One dense sentence with the resource and returned fields front-loaded, followed by a short provenance clause. No filler, no restatement of the title.

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?

For a one-parameter read-only tool with no output schema, the description supplies the frame, the body list, the returned quantities, the valid date window, and accuracy provenance — enough to call it correctly. The only gap is behavior on out-of-range input or malformed times, which the agent must infer.

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% and the single parameter already documents ISO 8601 UTC and the 'now' default, so the schema carries the syntax. The description still adds non-obvious semantics by imposing the 1800–2200 valid range, a constraint the schema does not encode.

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?

States a concrete resource (tropical zodiac positions of the Sun, Moon, Mercury–Pluto, mean North Node, mean Black Moon Lilith) with the exact quantities returned (longitude, sign, degree, daily speed, retrograde flag) and a specific temporal scope (a UTC instant between 1800 and 2200). An agent can distinguish this from a 'current sky' or 'birth placements' tool 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?

The phrase 'at a UTC instant' implies this is the tool for an arbitrary requested moment, and the 1800–2200 bound implicitly excludes out-of-range queries, but no sibling is named and no explicit when-not guidance is given. Nothing tells the agent when to prefer get_current_sky or get_birth_placements instead.

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