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Perigee

by io.github.dlamarre-dev
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Position and velocity

perigee_state
Read-only

Position (km, ICRF/J2000 equatorial axes) and velocity (km/s) of an object at a date, relative to a centre (default: the body it orbits or stands on), with distance, altitude above the centre, speed, light time, whether it is in sunlight, and provenance. Around the Earth, the Moon or Mars it also gives the ground point below it (latitude, longitude; on the Earth the country or sea, e.g. "over Brazil", "over the Indian Ocean").

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "id": "<id>"
    },
    "name": "perigee_state"
  }
}

Input Schema

NameRequiredDescriptionDefault
idYesObject id from perigee_find (NORAD number, mission id, planet, "moon:<id>", "site:<id>", "launch:<id>", "star:<id>", "comet:<id>", "asteroid:<id>" or a dwarf planet name), e.g. "25544" for the ISS.
dateNoISO 8601 UTC instant, e.g. 2026-12-01T00:00:00Z (default: now).
centreNoReference object id, e.g. "earth", "sun", "moon:moon", "mars".

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A3.8/5.0
Behavior4/5

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

Annotations already declare readOnlyHint and openWorldHint, so the bar is lower; the description still adds real value by disclosing the default centre (the body orbited or stood on) and the conditional ground-point behaviour for Earth/Moon/Mars. It does not discuss precision, error or failure behaviour, which keeps it from 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.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single dense sentence, front-loaded with the primary quantity and units, with secondary outputs trailing. It is information-rich but long, and the parenthetical enumeration of returned fields makes it slightly heavy to scan.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description must convey the return shape, and it does so thoroughly: position, velocity, distance, altitude, speed, light time, sunlit status, provenance, and conditional ground point. Missing only edge-case behaviour and the precise frame/epoch caveats of the returned vectors.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds the default rule for centre beyond the schema's bare example list. The date default (now) is only in the schema, so the description does not fully carry the parameter story on its own.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

Specific resource and quantity: position in km on ICRF/J2000 axes plus velocity in km/s, relative to a centre. It is clearly distinct in content from scalar siblings like perigee_distance and perigee_orbit, though no sibling is named explicitly, so it falls just 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.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the described output (a full state vector at a date) but there is no explicit when-to-use or when-not guidance, and no pointer to perigee_distance, perigee_orbit or perigee_ground_track for the overlapping cases.

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

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