Astro Agents - verifiable planetary timing data and astrology

Natal chart (birth chart)

natal_chart

Read-onlyIdempotent

Western astrology natal chart (birth chart, horoscope): planets in zodiac signs and houses, sun sign, moon sign and rising sign (ascendant), MC, aspects and a summary. Everything a natal reading needs, computed exactly: positions, house cusps (Placidus by default; Koch, Whole Sign, Equal, Porphyry, Regiomontanus, Campanus, Topocentric, Alcabitius, Morinus, Meridian), ascendant/MC/DSC/IC, aspects with orbs and applying/separating state, element and modality balance, chart ruler, sect and Part of Fortune. Deterministic (JPL DE440, no LLM); every result carries meta.result_sha256. Price $0.06 per call via REST POST https://astro-agent.dev/v1/western/natal (x402 or MPP); always paid, never a free call.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "latitude": "<latitude>",
      "longitude": "<longitude>"
    },
    "name": "natal_chart"
  }
}

Input Schema

Name	Required	Description	Default
`date`	No	YYYY-MM-DD (use with 'time' instead of 'datetime').
`time`	No	HH:MM or HH:MM:SS, 24 h. Omit if unknown (computed at 12:00 with a TIME_UNKNOWN warning).
`options`	No	Optional calculation settings; every default is the common Western convention.
`datetime`	No	Local birth date-time, ISO 8601: '1990-05-15T14:30' (local clock time at the place) or with an explicit offset '1990-05-15T14:30:00+02:00'. Alternative: 'date' + 'time'.
`latitude`	Yes	Decimal degrees, north positive.
`timezone`	No	IANA zone, e.g. 'Asia/Kolkata'. Optional: resolved from the coordinates, with the historical offset (DST, Local Mean Time) of that date.
`longitude`	Yes	Decimal degrees, east positive.
`time_basis`	No	What the given clock time is: civil wall-clock (default), UTC, Local Mean Time, or true (apparent) solar time.	civil
`ambiguous_time`	No	Which occurrence to use when a local time happens twice (DST fall-back).	earlier

Output Schema

Name	Required	Description
`meta`	No	Provenance of the result.
`error`	No	x402 offer only: why payment is required.
`result`	No	The calculation result.
`accepts`	No	x402 offer only: the payment options (scheme, network, amount, asset, payTo, ...).
`endpoint`	No	The REST route that computed it, e.g. 'western/natal'.
`resource`	No	x402 offer only: the resource being paid for.
`extensions`	No	x402 offer only: protocol extensions (bazaar).
`x402Version`	No	x402 offer only: protocol version (2).

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedNov 3, 2026

addedOutput schema / anyOf

Added value: +[
+  {
+    "required": [
+      "endpoint",
+      "result",
+      "meta"
+    ]
+  },
+  {
+    "required": [
+      "x402Version",
+      "accepts"
+    ]
+  }
+]

addedOutput schema / properties / accepts

Added value: +{
+  "description": "x402 offer only: the payment options (scheme, network, amount, asset, payTo, ...).",
+  "items": {
+    "type": "object"
+  },
+  "minItems": 1,
+  "type": "array"
+}

addedOutput schema / properties / error

Added value: +{
+  "description": "x402 offer only: why payment is required.",
+  "type": "string"
+}

addedOutput schema / properties / extensions

Added value: +{
+  "description": "x402 offer only: protocol extensions (bazaar).",
+  "type": "object"
+}

addedOutput schema / properties / resource

Added value: +{
+  "description": "x402 offer only: the resource being paid for.",
+  "type": "object"
+}

addedOutput schema / properties / x402Version

Added value: +{
+  "description": "x402 offer only: protocol version (2).",
+  "type": "integer"
+}

removedOutput schema / required

Removed value: -[
-  "endpoint",
-  "result",
-  "meta"
-]

Changed1 schema field changedOct 6, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "endpoint": {
+      "description": "The REST route that computed it, e.g. 'western/natal'.",
+      "type": "string"
+    },
+    "meta": {
+      "description": "Provenance of the result.",
+      "properties": {
+        "astronomy_library": {
+          "description": "Astronomy library and version.",
+          "type": "string"
+        },
+        "compute_ms": {
+          "description": "Computation time in milliseconds.",
+          "type": "number"
+        },
+        "computed_at": {
+          "description": "When it was computed (UTC, ISO 8601).",
+          "type": "string"
+        },
+        "deterministic": {
+          "description": "Always true: same input, same result.",
+          "type": "boolean"
+        },
+        "engine": {
+          "description": "Engine name and version.",
+          "type": "string"
+        },
+        "ephemeris": {
+          "description": "Ephemeris used (NASA/JPL DE440).",
+          "type": "string"
+        },
+        "frame": {
+          "description": "Reference frame of the positions.",
+          "type": "string"
+        },
+        "input_sha256": {
+          "description": "SHA-256 of the canonical input.",
+          "type": "string"
+        },
+        "llm_used": {
+          "description": "Always false: no language model is involved.",
+          "type": "boolean"
+        },
+        "payment": {
+          "description": "How this call was paid: protocol ('free' or 'none'), price and the free calls remaining.",
+          "type": "object"
+        },
+        "reproducibility": {
+          "description": "How to reproduce and check this result.",
+          "type": "string"
+        },
+        "result_sha256": {
+          "description": "SHA-256 of the canonical 'result'; check it with verify_result_hash.",
+          "type": "string"
+        }
+      },
+      "required": [
+        "engine",
+        "deterministic",
+        "llm_used",
+        "input_sha256",
+        "result_sha256"
+      ],
+      "type": "object"
+    },
+    "result": {
+      "description": "The calculation result.",
+      "properties": {
+        "angles": {
+          "description": "Ascendant, midheaven, descendant and imum coeli, each with longitude and sign.",
+          "type": "object"
+        },
+        "aspects": {
+          "description": "Aspects between two points: point_a, point_b, aspect name, exact angle, orb, allowed orb, exactness percentage and whether it is applying or separating.",
+          "type": "array"
+        },
+        "houses": {
+          "description": "The twelve house cusps: longitude, sign, degree in sign, element and modality.",
+          "type": "array"
+        },
+        "points": {
+          "description": "One entry per body or point (Sun to Pluto, lunar nodes, Chiron...): ecliptic longitude, sign, degree in sign, element, modality, latitude, daily speed, retrograde flag, distance in AU and, with a location, the house.",
+          "type": "array"
+        },
+        "settings": {
+          "description": "Settings applied: zodiac, house system and the aspect set with its orbs.",
+          "type": "object"
+        },
+        "sidereal_time": {
+          "description": "Local sidereal time as ARMC (degrees) and the true obliquity of the ecliptic.",
+          "type": "object"
+        },
+        "subject": {
+          "description": "The resolved input: 'time' (local input, time zone and historical UTC offset, UT, Julian days, Delta T) and, when given, 'location' (latitude, longitude).",
+          "type": "object"
+        },
+        "summary": {
+          "description": "Key facts: Sun, Moon and rising signs, element and modality balance, retrograde planets, chart ruler, day or night chart (sect) and the Part of Fortune.",
+          "type": "object"
+        },
+        "warnings": {
+          "description": "Notes on the input or the calculation (for example an assumed noon for an unknown birth time). Present only when there is something to say.",
+          "type": "array"
+        }
+      },
+      "required": [
+        "subject",
+        "settings",
+        "angles",
+        "houses",
+        "sidereal_time",
+        "points",
+        "aspects",
+        "summary"
+      ],
+      "type": "object"
+    }
+  },
+  "required": [
+    "endpoint",
+    "result",
+    "meta"
+  ],
+  "type": "object"
+}

Changed4 schema fields changedOct 5, 2026

addedInput schema / properties / options / description

Added value: +"Optional calculation settings; every default is the common Western convention."

addedInput schema / properties / options / properties / house_system / description

Added value: +"House system for cusps and planet houses, e.g. 'placidus' (default) or 'whole_sign'."

addedInput schema / properties / options / properties / luminary_orb_bonus / description

Added value: +"Extra orb in degrees for aspects involving the Sun or the Moon. Example: 2."

addedInput schema / properties / options / properties / zodiac / description

Added value: +"'tropical' (Western, default) or 'sidereal' (pair it with 'ayanamsa')."

First observedOct 3, 2026

TDQS

A4.2/5.0

Behavior5/5

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

Goes well beyond the annotations: declares determinism (JPL DE440, no LLM), states every result carries meta.result_sha256, discloses the exact REST endpoint, the payment mechanism (x402 or MPP) and the $0.06 per-call cost with 'always paid, never a free call'. This is the kind of operational context an agent cannot get from readOnlyHint/idempotentHint alone.

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?

Purpose is front-loaded in the first clause, then output contents, then determinism/pricing/logistics — a sensible order. It is dense and the second sentence is a long run-on that partly duplicates the schema's house-system enum, but almost every element is load-bearing for calling or budgeting the call.

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 9-parameter, nested-schema, paid, output-schema-bearing tool, the description covers what is computed, how it is computed, what it costs, and how to reach it. Return values need not be explained because an output schema exists, and the hash/price details fill the remaining gaps an agent would otherwise have to guess.

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% with enums and defaults documented inline, so the schema already carries parameter meaning. The description restates conventions ('Placidus by default', listed house systems, aspects with orbs) but adds no syntax or interpretation beyond what the schema provides.

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+resource: a Western astrology natal chart with planets in signs/houses, luminaries, ascendant/MC, aspects and summary. The 'Western' qualifier plus the enumerated outputs let an agent separate it from Vedic siblings (kundli, kundli_full, vedic_report) and from narrower tools like planet_positions or aspects.

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

Usage Guidelines3/5

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

Usage is implied by 'Everything a natal reading needs' and by the Western/sidereal option, so the agent can infer this is the full-chart tool. But there is no explicit 'use this instead of X' routing, no stated exclusions, and no mention of when a narrower sibling (planet_positions, aspects, planetary_lines) would be preferable.

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

All Astro Agents - verifiable planetary timing data and astrology tools Inspect

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