Horizons Nasa

Ephemeris

ephemeris

Read-onlyIdempotent

Generate an ephemeris (default observer table).

Input Schema

Name	Required	Description
`center`	No	Default "500@399" (geocentric).
`command`	Yes	SPK id, name, or designation. e.g. "499" (Mars).
`step_size`	No	e.g. "1h", "1d" (default "1h").
`stop_time`	Yes	e.g. "2026-05-19"
`start_time`	Yes	e.g. "2026-05-18"
`table_type`	No	OBSERVER (default) \| VECTORS \| ELEMENTS

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "command": "499",
+    "start_time": "2026-05-18",
+    "stop_time": "2026-05-19"
+  },
+  {
+    "command": "10",
+    "start_time": "2026-01-01",
+    "step_size": "1d",
+    "stop_time": "2026-01-31",
+    "table_type": "VECTORS"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "Ephemeris data from JPL Horizons",
+  "type": "object"
+}

First observedMay 18, 2026

TDQS

B3.2/5.0

Behavior3/5

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

Annotations already cover readOnly, openWorld, idempotent, and non-destructive behavior. The description adds 'default observer table,' which is consistent with the schema but does not provide additional behavioral context.

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?

Single sentence, front-loaded, and efficient. No wasted words, but could be slightly more informative without losing conciseness.

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

Completeness3/5

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

Given the complete schema and annotations, the description is minimally adequate. However, it does not explain what the output contains or when to choose different table types.

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 baseline applies. The description does not add meaning beyond the schema; 'default observer table' is already in the table_type description.

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?

The description clearly states the tool's function: 'Generate an ephemeris (default observer table).' It specifies a verb and resource, but does not explicitly distinguish from sibling tools like 'observers' or 'vectors'.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

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

No guidance on when to use this tool versus alternatives. Lacks context, prerequisites, or exclusions.

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

All Horizons Nasa tools Inspect

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