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caelus-mcp

by io.github.heavyblotto

natal_chart

A person's birth chart. Requires their exact birth date+time and birthplace (all three: date, lat, lon). Use this — not current_sky — whenever the question is about someone's natal/birth chart. Returns 13 bodies (sun–pluto, chiron, nodes) with sign, house, retrograde, speed; ASC/MC; cusps; major aspects with orb, applying/separating phase, and strength (1=exact). Vs Swiss Ephemeris (1850–2150): Sun–Saturn ≤1″, Uranus ≤1.9″, Neptune ≤4.6″, Moon ≤2.5″, Pluto ≤3.4″ (Chebyshev pack), Chiron ≤1″, mean node ≤1″, true node ≤ 1′ vs SE's built-in ephemeris.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
latYesLatitude, north positive
lonYesLongitude, EAST positive (Americas are negative)
dateYesUTC date-time, ISO 8601, e.g. 1990-06-10T14:30:00Z. Convert local birth time to UTC first.
gridNoCanonical grid (with output:'canonical'): arcsec (default), milliarcsec, centideg, dms ([deg,min,sec] triples), or accuracy (each body snapped to its measured validated accuracy — the most portable choice for cross-platform content addressing)arcsec
outputNo'float' (default) returns the usual floating-point payload. 'canonical' returns integers on a declared grid plus a sha256 digest: stable across machines/browsers/languages, hashable for caching and dedupe, precision-honest, with sign/house/aspects re-derived from the quantized values so displayed numbers and facts always agreefloat
zodiacNotropical (default) or sidereal:<ayanamsa>tropical
remaindersNoWith output:'canonical': also return the remainder set — the integer sub-quantum residues quantization discarded, keyed by leaf path and bound to the payload digest. 'auto' picks one grid finer than the base; or name the refinement grid (must be strictly finer). Residues telescope: composeRemainders(payload, remainders) rebuilds the finer-grid payload exactly. Time residues are integer microseconds, distance residues integer nano-AU
separationNoAspect separation: 'longitude' (default, the zodiacal aspect) or 'spatial' (true great-circle separation accounting for ecliptic latitude — differs for the Moon, Pluto, and bodies far off the ecliptic)longitude
house_systemNoHouse system (default placidus). Case- and spacing-insensitive; valid: placidus, whole_sign, equal, porphyry, koch, regiomontanus, campanus, alcabitius, morinus, meridian, polich_page, vehlow (aliases like "whole sign" also work).placidus

TDQS

A4.5/5.0
Behavior5/5

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

No annotations are provided, so the description fully carries the transparency burden. It discloses what the tool returns (13 bodies, ASC/MC, cusps, aspects with orb and phase), the requirement for exact birth data, and extensive numerical accuracy bounds vs Swiss Ephemeris. This is rich behavioral context.

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 front-loaded with the core purpose, followed by a usage directive, return summary, and accuracy spec. Every sentence adds value, and the accuracy sentence is technical but necessary. No fluff or redundancy.

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?

The tool is complex (9 params, no output schema), yet the description covers the core domain (natal chart), requirements, return contents, and precision guarantees. It does not need to explain parameters because the schema handles that. The description is complete for a well-schematized tool.

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%, so the schema already documents all 9 parameters in detail. The description reinforces the need for all three required params (date, lat, lon) but does not add meaning beyond what the schema provides. Baseline 3 is appropriate.

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 clearly identifies the tool as computing a person's birth chart, states the required inputs (date, lat, lon), and directly contrasts it with current_sky for natal chart questions. This distinguishes it from siblings and makes the purpose unambiguous.

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

Usage Guidelines4/5

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

The description explicitly states when to use this tool ('whenever the question is about someone's natal/birth chart') and explicitly warns against using current_sky in those cases. It could mention more alternatives (e.g., synastry, composite) but the primary usage confusion is addressed.

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

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TDQS

A3.9/5.0
Disambiguation5/5

Each tool has a highly specific and well-described purpose. Despite the large number, their functions are clearly distinct—e.g., natal_chart vs current_sky vs composite, or dasha vs firdaria vs profections vs releasing. The detailed descriptions prevent ambiguity.

Naming Consistency3/5

Names are consistently in snake_case but vary in style: some are noun phrases (natal_chart, cosmic_weather), some are verb-like (releasing, returns), and some are descriptive (aspect_patterns, find_aspect_dates). There is no strict verb_noun pattern, leading to moderate consistency.

Tool Count4/5

34 tools is high but appropriate for a comprehensive astrology API covering natal, transits, progressions, returns, synastry, time-lord techniques, sky events, and synthetic bodies. Each tool serves a specific niche, so the count feels justified rather than excessive.

Completeness5/5

The tool surface is extremely thorough, covering all major areas of astrology: chart generation, aspects, configurations, dignities, time-lord techniques (multiple systems), synastry, composite, progressions, returns, transits, sky events, rectification, electional, and synthetic bodies. No obvious gaps for the intended domain.

Resources