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

The description discloses far more than the annotations already provide: parallax/aberration correction, refraction-corrected horizontal coordinates, defaults for elevation and time, the UTC interpretation of zone-less time strings, the differing behavior for solar-system bodies (body card included) versus catalog stars (no card, field absent), and the explicit note that the server does not geocode. These are valuable behavioral traits beyond readOnly/idempotent hints, with no contradiction to the 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 long but every sentence carries information. It opens with the core function, then lists outputs, then surfaces usage constraints and defaults, and closes with the geocoding caveat. There is no filler or repetition; the dense structure is front-loaded and well ordered.

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 tool with 7 parameters and an output schema, the description is remarkably complete. It covers all required parameters and defaults, the body/star selection model, timezone handling, geocoding limitations, and the difference in return shape between solar-system bodies and stars. Even though an output schema exists, the description adds context that no structured field captures, leaving no critical gap for correct invocation.

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 baseline is 3. The prose adds genuinely useful semantics on top: the precedence rule between `star` and `body`, the fact that only solar-system bodies return a body card, and the clarification that `time` without a zone is read as UTC. These go beyond the schema and materially help an agent call the tool correctly, earning a 4.

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 clearly states the verb and resource: compute the apparent topocentric position of a solar-system body or named star for a given observer and instant, and lists the many returned coordinate systems and derived quantities. It is specific enough to distinguish from generic astronomy queries, but it does not explicitly differentiate from siblings such as astronomy_get_ephemeris or astronomy_get_rise_set, so the purpose is clear but the sibling distinction is not explicit.

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 useful usage directives: how to select a star versus body, the precedence of `star` over `body`, default time and elevation, and the external requirement that geocoding must be done upstream. However, it never says when to choose this tool over astronomy_get_ephemeris (which likely covers time ranges) or astronomy_get_rise_set, leaving relative usage to inference. It covers some usage conditions but omits explicit alternatives.

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