astronomy-mcp-server

astronomy-mcp-server: get small-body ephemeris

astronomy_get_ephemeris

Read-onlyIdempotent

Fetch a time-series ephemeris for a small body (asteroid or comet) or spacecraft from JPL Horizons — RA/Dec, distance, and apparent magnitude over a span, optionally with observer-relative altitude/azimuth. This covers objects the in-process major-body set cannot. The designation is passed to Horizons verbatim, so it must be in a form Horizons resolves to a single record: a numbered asteroid takes a trailing-semicolon record lookup (e.g. "433;" for Eros, "1;" for Ceres), and a periodic comet takes the DES + closest-apparition form (e.g. "DES=1P;CAP" for Halley). Spacecraft take their negative SPK-ID. Anything else goes through the Horizons name search: a bare name matching nothing (e.g. "433 Eros") or several records (e.g. "1P/Halley") is rejected, but one matching a single object succeeds even when that object is not the one meant — "Eros" resolves to Kerberos, a moon of Pluto — so compare target_name, the object Horizons resolved, with the one intended. start and stop are ISO 8601 UTC and stop must be after start; step is a count plus a unit of m, h, d, mo, or y, such as "1d", "1h", or "10m". Supplying observer latitude/longitude yields topocentric coordinates and adds alt/az — supply both or neither. This is a gated, network-backed extension (JPL Horizons is keyless but rate-limited and best-effort); large spans truncate inline at 200 rows, and the truncation notice names the exact start to resume from — one step past the last row returned, because Horizons includes the start instant in its output — so re-calling from there continues the series without repeating a sample. Splitting the range into smaller adjacent spans works too; keep the same step either way so no sample is lost.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`step`	No	Step size as a positive count plus a unit of m (minutes), h (hours), d (days), mo (months), or y (years), e.g. "10m", "1h", "1d". Default "1h".	1h
`stop`	No	Ephemeris stop as an ISO 8601 UTC string, and must be later than start. Defaults to 24 hours after start. A value with no zone designator is read as UTC, not the local zone of the server process.
`start`	No	Ephemeris start as an ISO 8601 UTC string, e.g. "2024-01-01T00:00:00Z". Defaults to now. A value with no zone designator is read as UTC, not the local zone of the server process.
`latitude`	No	Observer latitude in decimal degrees — supply together with longitude for topocentric coordinates and alt/az. Supplying one without the other is rejected.
`elevation`	No	Observer elevation in meters above sea level. Default 0.
`longitude`	No	Observer longitude in decimal degrees. Supply together with latitude; one without the other is rejected.
`designation`	Yes	JPL Horizons target, passed verbatim — use a form that resolves to one record. Numbered asteroid: trailing-semicolon record lookup, e.g. "433;" (Eros), "1;" (Ceres). Periodic comet: DES + closest-apparition flag, e.g. "DES=1P;CAP" (Halley), "DES=2P;CAP" (Encke). Spacecraft: negative SPK-ID, e.g. "-48" (Hubble). A bare name like "433 Eros" (no match) or "1P/Halley" (several records) is rejected, but one matching a single object succeeds even when it is not the object meant — check `target_name` in the result. Look up designations at ssd.jpl.nasa.gov/tools/sbdb_lookup.html.

Output Schema

TableJSON Schema

Name	Required	Description
`cap`	No	The inline row cap that was applied.
`error`	No	Present when the call failed. Absent on success.
`shown`	No	Number of ephemeris rows returned.
`notice`	No	Caveats on the returned series — how to retrieve rows omitted by the cap, and whether any rows were dropped. Absent when the whole span came back intact.
`points`	No	Time-series of positions, one per step, in chronological order.
`dropped`	No	Rows Horizons returned that carried no usable time, position, or distance and were dropped. Present only when at least one row was dropped, in which case the series has gaps and is shorter than the requested step count.
`truncated`	No	True when Horizons returned more rows than the inline cap.
`designation`	No	The body designation echoed from the request.
`target_name`	No	The object JPL Horizons resolved the designation to, from its 'Target body name' header — compare it with the intended object, since a bare name can resolve to a different one. Absent when Horizons' response names no target.

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedSep 24, 2026

changedInput schema / properties / designation / description

Previous value: -"JPL Horizons target, passed verbatim — use a form that resolves to one record. Numbered asteroid: trailing-semicolon record lookup, e.g. \"433;\" (Eros), \"1;\" (Ceres). Periodic comet: DES + closest-apparition flag, e.g. \"DES=1P;CAP\" (Halley), \"DES=2P;CAP\" (Encke). Spacecraft: negative SPK-ID, e.g. \"-48\" (Hubble). A bare name like \"433 Eros\" or \"1P/Halley\" fails. Look up designations at ssd.jpl.nasa.gov/tools/sbdb_lookup.html."New value: +"JPL Horizons target, passed verbatim — use a form that resolves to one record. Numbered asteroid: trailing-semicolon record lookup, e.g. \"433;\" (Eros), \"1;\" (Ceres). Periodic comet: DES + closest-apparition flag, e.g. \"DES=1P;CAP\" (Halley), \"DES=2P;CAP\" (Encke). Spacecraft: negative SPK-ID, e.g. \"-48\" (Hubble). A bare name like \"433 Eros\" (no match) or \"1P/Halley\" (several records) is rejected, but one matching a single object succeeds even when it is not the object meant — check `target_name` in the result. Look up designations at ssd.jpl.nasa.gov/tools/sbdb_lookup.html."

changedOutput schema / properties / error / properties / data / properties / reason / description

Previous value: -"Machine-readable failure mode. Declared by this tool: `invalid_time`: The start or stop timestamp is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `invalid_time_range`: The resolved stop instant is at or before the resolved start instant. `incomplete_observer`: Exactly one of latitude and longitude was supplied. `invalid_step`: The step is not a positive count followed by a unit of m, h, d, mo, or y. `body_not_found`: JPL Horizons has no match for the designation, or the designation is ambiguous (a bare comet name matches multiple apparition records). `horizons_unavailable`: The JPL Horizons API failed after retries. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `invalid_time`: The start or stop timestamp is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `invalid_time_range`: The resolved stop instant is at or before the resolved start instant. `incomplete_observer`: Exactly one of latitude and longitude was supplied. `invalid_step`: The step is not a positive count followed by a unit of m, h, d, mo, or y. `time_out_of_range`: The requested span falls outside the target's Horizons data span. The message names the bound Horizons reported, e.g. after A.D. 2599-DEC-31 for Mars. `body_not_found`: JPL Horizons has no match for the designation, or the designation is ambiguous (a bare comet name matches multiple apparition records). `horizons_unavailable`: The JPL Horizons API failed after retries. Other values are possible when a failure originates below the handler."

changedOutput schema / properties / error / properties / data / properties / reason / examples

Previous value: -[
-  "invalid_time",
-  "invalid_time_range",
-  "incomplete_observer",
-  "invalid_step",
-  "body_not_found",
-  "horizons_unavailable"
-]New value: +[
+  "invalid_time",
+  "invalid_time_range",
+  "incomplete_observer",
+  "invalid_step",
+  "time_out_of_range",
+  "body_not_found",
+  "horizons_unavailable"
+]

addedOutput schema / properties / target_name

Added value: +{
+  "description": "The object JPL Horizons resolved the designation to, from its 'Target body name' header — compare it with the intended object, since a bare name can resolve to a different one. Absent when Horizons' response names no target.",
+  "type": "string"
+}

Changed2 schema fields changedSep 19, 2026
- removedOutput schema / properties / points / items / properties / magnitude / anyOf
```
Removed value: -[
-  {
-    "type": "number"
-  },
-  {
-    "type": "null"
-  }
-]
```
- addedOutput schema / properties / points / items / properties / magnitude / type
```
Added value: +[
+  "number",
+  "null"
+]
```

Changed6 schema fields changedAug 25, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedInput schema / additionalProperties
```
Added value: +false
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedOutput schema / anyOf

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "designation",
+      "points",
+      "truncated",
+      "shown",
+      "cap"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / error

Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `invalid_time`: The start or stop timestamp is not a parseable ISO 8601 instant, or names a calendar date that does not exist (e.g. 2026-02-30). `invalid_time_range`: The resolved stop instant is at or before the resolved start instant. `incomplete_observer`: Exactly one of latitude and longitude was supplied. `invalid_step`: The step is not a positive count followed by a unit of m, h, d, mo, or y. `body_not_found`: JPL Horizons has no match for the designation, or the designation is ambiguous (a bare comet name matches multiple apparition records). `horizons_unavailable`: The JPL Horizons API failed after retries. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "invalid_time",
+            "invalid_time_range",
+            "incomplete_observer",
+            "invalid_step",
+            "body_not_found",
+            "horizons_unavailable"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}

removedOutput schema / required

Removed value: -[
-  "designation",
-  "points",
-  "truncated",
-  "shown",
-  "cap"
-]

Changed2 schema fields changedAug 18, 2026

changedInput schema / properties / start / description

Previous value: -"Ephemeris start as an ISO 8601 UTC string, e.g. \"2024-01-01T00:00:00Z\". Defaults to now."New value: +"Ephemeris start as an ISO 8601 UTC string, e.g. \"2024-01-01T00:00:00Z\". Defaults to now. A value with no zone designator is read as UTC, not the local zone of the server process."

changedInput schema / properties / stop / description

Previous value: -"Ephemeris stop as an ISO 8601 UTC string, and must be later than start. Defaults to 24 hours after start."New value: +"Ephemeris stop as an ISO 8601 UTC string, and must be later than start. Defaults to 24 hours after start. A value with no zone designator is read as UTC, not the local zone of the server process."

First observedAug 18, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Even though annotations already declare readOnlyHint=true, openWorldHint=true, and idempotentHint=true, the description adds substantial behavioral context: the tool is gated and network-backed, Horizons is keyless but rate-limited and best-effort, large spans truncate at 200 rows, and the truncation notice names the exact start to resume from. There is no contradiction; the description enriches the annotation profile meaningfully.

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?

The description is long but every sentence earns its place given the tool's complexity. It front-loads the core purpose in the first sentence, then layers the necessary resolution rules, validation constraints, network behavior, and pagination details in a logical order. There is no filler or repetition of schema fields.

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

Completeness5/5

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

For a complex, network-backed, gated tool with 7 parameters and an output schema, the description is remarkably complete. It covers designation resolution, date/step constraints, topocentric coordinates, rate-limiting, truncation, and resumption strategy. Since an output schema exists, the description does not need to explain return values, and nothing essential is missing.

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 description coverage is 100%, so the baseline is 3, but the description adds value beyond the schema by explaining the trailing-semicolon asteroid convention, DES+CAP comet forms, negative SPK-ID for spacecraft, and the ambiguity pitfall with examples like '433 Eros' and 'Eros'. It reinforces the start/stop/step semantics and the topocentric coordinate coupling rule, making the parameters more usable than the schema alone.

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

Purpose5/5

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

The description begins with a precise verb and resource: 'Fetch a time-series ephemeris for a small body (asteroid or comet) or spacecraft from JPL Horizons.' It specifies the output dimensions (RA/Dec, distance, magnitude, optional alt/az) and clearly differentiates the tool by stating it covers objects the in-process major-body set cannot, which distinguishes it from sibling tools like astronomy_get_sky_position.

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

Usage Guidelines5/5

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

The description gives extensive when-to-use guidance: small bodies and spacecraft not in the major-body set. It also covers when-not-to-use scenarios, such as ambiguous or unmatched designations, and even explains how to verify the resolved target via `target_name`. This goes well beyond mere context and provides actionable selection criteria.

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

All astronomy-mcp-server tools Inspect

Try in Browser

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Glama MCP Gateway

Add one secure layer between your agents and this server.