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

TableJSON 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". 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	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.

Output Schema

TableJSON 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 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 and non-destructive, so safety is covered. The description adds useful behavioral context: the response varies with location ('with a location, sun times'), signalling that omitting location changes the result set. It stops short of noting the attribution/credit obligation that place resolution triggers (that lives in the schema), which keeps it off a 5.

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?

Two sentences, both front-loaded: the scope statement leads, then the sibling-routing clause. No filler, no repetition of schema content, and the broad-vs-narrow decision is placed before the alternatives.

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?

Output schema exists, so return values need not be described here, and all five parameters are documented in the schema. For a zero-required-parameter, read-only snapshot tool, the description gives everything an agent needs to pick it over the nine siblings and call it correctly.

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%, so tz, lat, lon, date, and place are all fully documented in the input schema, including the UTC/JD date formats and the 1700-2200 range guard. The description only hints that location is optional via '(with a location) sun times', adding nothing the schema does not already carry.

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?

Specific verb+resource ('one-call snapshot of the whole sky for a place and moment') followed by an enumeration of exactly what is returned: moon phase and illumination, visible planets, next eclipse, sun times. It is immediately distinguishable from astro_moon, astro_positions, and astro_sun by the breadth of its output.

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 when-to-use ('Reach for this first when the question is broad, like "what is in the sky tonight"') plus three named alternatives with the condition that selects each: astro_sun for solar-day detail, astro_dark_window for picking 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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