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

Annotations already cover read-only and open-world behavior, and the description adds genuinely non-obvious semantics: mean elements for Earth satellites vs instantaneous two-body elements otherwise, plus which reference frame inclination is measured in. It omits failure behavior for objects with no orbit solution, which keeps it off 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?

The output contents lead, then the regime distinction and framing rules follow, so it is front-loaded and information-dense. The second clause is long and compound, but every clause carries distinct semantic content.

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 no output schema, the description usefully enumerates return quantities, so an agent knows what comes back. However, the only required parameter ('id') is never explained — name vs catalog number vs SPICE identifier — and how the tool decides Earth-satellite vs other-object behavior is left unstated.

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 67% and the description adds real meaning beyond it: the 'centre' default is the body the object orbits, and the inclination reference frame differs by centre (equator vs ecliptic around the Sun). The required 'id' parameter remains undocumented in both places, which is the main gap.

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 names the resource (an object's orbit) and enumerates exactly what is returned: perigee/apogee altitudes, period, inclination, eccentricity, semi-major axis. That is specific enough to separate it from perigee_state (state vectors) or perigee_distance, but no sibling is named explicitly, so it stops short of a 5.

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 only implied by the regime split: Earth satellites get mean elements from a published element set, everything else gets instantaneous two-body elements at a date. It never says when to prefer this over perigee_state or perigee_object, nor any precondition such as the object needing a published element set.

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