CycleCalcs Astronomy

Precise positions of bodies

astro_positions

Read-onlyIdempotent

Exact positions for up to 20 bodies at an instant or over a time grid: right ascension and declination in both J2000 and of-date frames, ecliptic longitude and latitude, distance, and, with a location, altitude and azimuth with refraction stated per field. With a location the position is topocentric, but tropical_sign and constellation stay geocentric, and meta.conventions.label_origin says so. Use for "where exactly is X". Do not pass earth. For rise and set TIMES use astro_rise_set; for a visibility overview of all planets use astro_planet_board.

Input Schema

Name	Required	Description
`tz`	No	IANA timezone like "Europe/Lisbon" to render event times in local time. Optional; a resolved place supplies its own timezone.
`end`	No	Grid end. ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`lat`	No	Latitude in decimal degrees, north positive. Send lat and lon together.
`lon`	No	Longitude in decimal degrees, east positive (Lisbon is about -9.14). Send lat and lon together.
`date`	No	ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`step`	No	Grid stride, e.g. "1h", "10min", "1d".
`place`	No	The place NAME only, one to three words, instead of lat/lon: "City" or "City,CC" with an ISO country code, e.g. "Lisbon,PT". Never a question or a sentence. Resolved server-side; the response then carries a required GeoNames CC BY 4.0 credit in its attribution field, which must be preserved when shown.
`start`	No	Grid start (use with end and step). ISO 8601 UTC date or datetime, e.g. "2026-08-06" or "2026-08-06T21:00:00Z". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. "jd:2461000.5". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there.
`bodies`	Yes	Bodies to report. Each entry: One of sun, moon, mercury, venus, mars, jupiter, saturn, uranus, neptune, pluto, or a fixed J2000 target as "radec:RA,DEC" with RA in hours (0-24) and DEC in degrees (-90..90), e.g. "radec:5.6,-5.4" for the Orion Nebula region.
`cursor`	No	Opaque pagination cursor from a previous result's next_cursor. Send it with the same start/end arguments as the first page.

Output Schema

Name	Required	Description
`data`	Yes	Where each requested body is, at an instant or sampled across a range.
`rights`	No	Either unrestricted, or attribution_required when third-party place data was used. When attribution_required, the attribution line must be shown.
`warnings`	No	Machine-readable notices about this answer. Present only when non-empty. Never changes whether the call succeeded.
`attribution`	No	The credit line to display verbatim when rights is attribution_required.
`next_cursor`	No	Present only when more rows exist. Send it back with the SAME start/end arguments as the first call to get the next page.
`not_computed`	No	Data this API deliberately does not serve, and why. Present only when the question touched such a field. An absence named here is information: treat it as "withheld", never as "none exists".

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 23, 2026

changedInput schema / properties / place / description

Previous value: -"Place name instead of lat/lon, as \"City\" or \"City,CC\" with an ISO country code, e.g. \"Lisbon,PT\". Resolved server-side; the response then carries a required GeoNames CC BY 4.0 credit in its attribution field, which must be preserved when shown."New value: +"The place NAME only, one to three words, instead of lat/lon: \"City\" or \"City,CC\" with an ISO country code, e.g. \"Lisbon,PT\". Never a question or a sentence. Resolved server-side; the response then carries a required GeoNames CC BY 4.0 credit in its attribution field, which must be preserved when shown."

Changed3 schema fields changedOct 23, 2026

changedInput schema / properties / date / description

Previous value: -"ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / end / description

Previous value: -"Grid end. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Grid end. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / start / description

Previous value: -"Grid start (use with end and step). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Grid start (use with end and step). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". With a location, a bare date means that date there: its day, its evening and its night. Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

Changed3 schema fields changedSep 27, 2026

changedInput schema / properties / date / description

Previous value: -"ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / end / description

Previous value: -"Grid end. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Grid end. ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

changedInput schema / properties / start / description

Previous value: -"Grid start (use with end and step). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."New value: +"Grid start (use with end and step). ISO 8601 UTC date or datetime, e.g. \"2026-08-06\" or \"2026-08-06T21:00:00Z\". Or jd: followed by a Julian Day on the UT scale, e.g. \"jd:2461000.5\". On astro_positions, date may list up to 24 datetimes separated by commas, answered in the order sent. Omit for the current moment. Years 1700 to 2200 only; outside that range the API refuses with DATE_OUT_OF_RANGE because the ephemeris is not reliable there."

Changed1 schema field changedAug 9, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": true,
+  "description": "The MCP projection of a CycleCalcs v2 response: the answer, plus the provenance a caller needs to use it honestly.",
+  "properties": {
+    "attribution": {
+      "description": "The credit line to display verbatim when rights is attribution_required.",
+      "type": "string"
+    },
+    "data": {
+      "additionalProperties": true,
+      "description": "Where each requested body is, at an instant or sampled across a range.",
+      "properties": {
+        "bodies": {
+          "description": "SINGLE MODE: one entry per body, with its coordinates.",
+          "type": "array"
+        },
+        "instant": {
+          "description": "SINGLE MODE: the instant evaluated.",
+          "type": "string"
+        },
+        "series": {
+          "description": "RANGE MODE: one sample per step, each holding every body.",
+          "type": "array"
+        },
+        "window": {
+          "description": "RANGE MODE: the range actually evaluated.",
+          "type": "object"
+        }
+      },
+      "type": "object"
+    },
+    "next_cursor": {
+      "description": "Present only when more rows exist. Send it back with the SAME start/end arguments as the first call to get the next page.",
+      "type": "string"
+    },
+    "not_computed": {
+      "description": "Data this API deliberately does not serve, and why. Present only when the question touched such a field. An absence named here is information: treat it as \"withheld\", never as \"none exists\".",
+      "type": "array"
+    },
+    "rights": {
+      "description": "Either unrestricted, or attribution_required when third-party place data was used. When attribution_required, the attribution line must be shown.",
+      "type": "string"
+    },
+    "warnings": {
+      "description": "Machine-readable notices about this answer. Present only when non-empty. Never changes whether the call succeeded.",
+      "type": "array"
+    }
+  },
+  "required": [
+    "data"
+  ],
+  "type": "object"
+}

First observedAug 9, 2026

TDQS

A4.2/5.0

Behavior3/5

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

The read-only/idempotent safety profile is already carried by annotations, and the description still adds real behavioral context: topocentric vs geocentric frame switching with a location, refraction flagged per field, meta.conventions.label_origin, the GeoNames attribution that must be preserved, and DATE_OUT_OF_RANGE outside 1700-2200. That is genuinely useful beyond the annotations, but the description never mentions the pagination cursor's role or the shape of grid results, so it is solid rather than complete.

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?

Front-loads what is returned, then the frame caveat, then the routing rules in two short refusals. Dense but every clause carries information an agent needs; no filler or restatement of the title.

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 a full output schema and annotations present, the description covers the non-obvious semantics (frames, refraction, attribution, date bounds). The remaining gap is the grid/pagination interplay (start/end/step vs cursor), which is left entirely to the schema.

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 coverage is 100% and the parameter descriptions are unusually rich (date/jd formats, comma lists up to 24 datetimes, body list including radec: syntax, place vs lat/lon), so the schema does the heavy lifting. The tool description adds only the topocentric-vs-geocentric consequence of supplying a location, which is a modest complement to the schema rather than new parameter detail.

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?

States a specific verb and resource (exact positions for up to 20 bodies) and enumerates the returned quantities: RA/Dec in J2000 and of-date, ecliptic lon/lat, distance, altitude/azimuth with refraction. It also names the sibling tools it is not (astro_rise_set, astro_planet_board), so an agent can route without opening a schema.

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?

Explicit selection rule: 'Use for "where exactly is X"', plus two named alternatives with the conditions that select them (rise/set TIMES, all-planet visibility overview). It also states a negative constraint, 'Do not pass earth', which is the main misuse to guard against.

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

All CycleCalcs Astronomy tools Inspect

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