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Perigee

by io.github.dlamarre-dev
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Distance between two objects

perigee_distance
Read-only

Centre-to-centre distance between two objects at a date (km and astronomical units) and the light travel time, with the provenance of both positions. Example: from "earth" to "mars".

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": {
      "from": "<from>",
      "to": "<to>"
    },
    "name": "perigee_distance"
  }
}

Input Schema

NameRequiredDescriptionDefault
toYesSecond object 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. "mars".
dateNoISO 8601 UTC instant, e.g. 2026-12-01T00:00:00Z (default: now).
fromYesFirst object 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. "earth".

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 only cover readOnly/openWorld safety. The description adds substantive behavior beyond that: returns are in km and AU, include light travel time, and carry provenance for both positions. It does not cover error behavior for unknown ids, which is the remaining gap.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

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

One dense sentence stating resource, units, extra outputs, and provenance, followed by a minimal example. Front-loaded and waste-free.

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 usefully discloses return units and extra fields, which is the main thing an agent needs. Missing only failure modes and the fact that an unknown id may error or resolve differently.

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

Parameters3/5

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

Schema description coverage is 100%, so from/to/date are already fully documented with accepted id formats and the date default. The description adds only the concrete earth/mars example, so baseline 3 is appropriate.

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?

States a precise computation (centre-to-centre distance between two objects at a date) plus the units and derived outputs (light travel time, position provenance). An agent can tell it apart from perigee_distance_series by the single-date framing, though siblings are never named explicitly.

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?

The example ("earth" to "mars") implies the expected call shape, but nothing says when to prefer this over perigee_distance_series, perigee_sky_conjunctions, or perigee_close_approach. Usage is only inferable, not stated.

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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