CycleCalcs Astronomy

Sky snapshot for a place and moment

astro_sky_today

Read-onlyIdempotent

One-call snapshot of the whole sky for a place and moment: moon phase and illumination, which planets are up and worth looking at, the next eclipse, and (with a location) sun times. Reach for this first when the question is broad, like "what is in the sky tonight". For solar-day detail use astro_sun; for choosing an observing night use astro_dark_window; for one planet's exact position use astro_positions.

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.
`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.
`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.

Output Schema

Name	Required	Description
`data`	Yes	A whole-sky snapshot for one place and moment.
`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."

Changed5 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."

changedOutput schema / properties / data / properties / planets_down / description

Previous value: -"Planets below the horizon now."New value: +"Planets below the horizon at the request instant."

addedOutput schema / properties / data / properties / planets_tonight

Added value: +{
+  "description": "Planets above this horizon after civil dusk ends or before civil dawn begins, brightest first, with the altitude each verdict was decided on. The list to answer \"what can I see tonight\" from; planets_up is not.",
+  "type": "array"
+}

addedOutput schema / properties / data / properties / planets_tonight_basis

Added value: +{
+  "description": "The civil dusk and civil dawn instants planets_tonight was sampled at, the solar altitude that defines them, and the kind of night (normal, never_dark, dark_all_day).",
+  "type": "object"
+}

changedOutput schema / properties / data / properties / planets_up / description

Previous value: -"Planets above the horizon now, brightest first."New value: +"Planets above the horizon at the request instant, brightest first, daylight included; each carries observable_tonight and a visibility phrase checked against this horizon at civil dusk and dawn."

Changed1 schema field 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."

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": "A whole-sky snapshot for one place and moment.",
+      "properties": {
+        "local_date": {
+          "description": "The local calendar date the snapshot describes.",
+          "type": "string"
+        },
+        "moon": {
+          "description": "Phase, illuminated fraction, and rise/set.",
+          "type": "object"
+        },
+        "next_events": {
+          "description": "The next notable sky events, soonest first.",
+          "type": "array"
+        },
+        "night": {
+          "description": "When true darkness begins and ends tonight.",
+          "type": "object"
+        },
+        "planets_down": {
+          "description": "Planets below the horizon now.",
+          "type": "array"
+        },
+        "planets_up": {
+          "description": "Planets above the horizon now, brightest first.",
+          "type": "array"
+        },
+        "summary": {
+          "description": "A one-line plain-language reading of the whole snapshot.",
+          "type": "string"
+        },
+        "sun": {
+          "description": "Sunrise, sunset and the Sun's current position.",
+          "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

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds genuine behavioral context beyond that: it aggregates eclipse, planet and lunar data in a single call, and that payload varies with whether a location is supplied ('with a location, sun times'). It stops short of describing response size or the attribution-preservation obligation, which lives only in the schema.

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?

Three sentences, zero waste: capability first, then the primary selection cue, then the exclusion routing. Every clause earns its place and the most important guidance is front-loaded.

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?

An output schema exists, so return-shape explanation is unnecessary; annotations carry the safety profile; the schema carries parameter detail. The description supplies exactly the decision layer the structured fields cannot: what it covers and how to choose it over nine siblings.

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%, including the place-vs-lat/lon distinction, the ISO/JD date formats and the 1700-2200 range, so the schema does the heavy lifting. The description only echoes the optionality of location via '(with a location)'. Baseline 3 applies.

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 ('One-call snapshot of the whole sky for a place and moment') and enumerates the contents: moon phase and illumination, visible planets, next eclipse, sun times. This is clearly distinguishable from the single-topic siblings it names.

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?

Explicitly routes broad questions here ('Reach for this first when the question is broad, like "what is in the sky tonight"') and names three alternatives with the exact condition that selects each: astro_sun for solar-day detail, astro_dark_window for choosing an observing night, astro_positions for one planet's exact position.

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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