# caelus-mcp MCP server

34-tool Caelus MCP for validated astrology: charts, transits, Vedic, facts, sky view, synthetic.

## Links
- Registry page: https://www.getdrio.com/mcp/io-github-heavyblotto-caelus-mcp
- Repository: https://github.com/heavyblotto/caelus

## Install
- Command: `npx -y caelus-mcp`
- Endpoint: https://www.ephemengine.com/api/mcp
- Auth: Not captured

## Setup notes
- Package: Npm caelus-mcp v0.23.0
- Remote endpoint: https://www.ephemengine.com/api/mcp

## Tools
- 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. Endpoint: https://www.ephemengine.com/api/mcp
- current_sky - The sky at a moment and place — not tied to any person. Use for "what's the sky/transits right now" or the chart of a non-birth event. Date defaults to now; lat/lon default to 0,0 (geocentric on the equator at the prime meridian), where houses and ASC/MC are nominal — pass a real location if houses matter. For a specific person's birth chart use natal_chart instead. Returns positions, houses, retrogrades, aspects. Endpoint: https://www.ephemengine.com/api/mcp
- sky_view - Where the visible bodies land in a framed photo of the sky, for an image prompt. Give a place, a moment, an aim (compass direction and altitude), a lens, and an image size; get each in-frame body's pixel position, apparent size, brightness, the Moon's phase orientation, a sky-state summary (twilight, limiting magnitude, horizon row), the bright bodies just outside the frame, a ready-to-use prompt, and a machine-readable `renderPlan` (a body-free background-plate prompt plus the computed layers to composite locally, for a hybrid render pipeline). Caelus computes the geometry and photometry; it does NOT render the image. For "at sunset", first find the set time with sky_events, then pass it as date. Endpoint: https://www.ephemengine.com/api/mcp
- sky_view_sequence - A time sequence of sky frames for an animation: the same place, aim, and lens stepped through time. Returns a compact per-frame timeline (instant, twilight, Sun/Moon altitude, Moon phase + bright-limb, whether the Milky Way is in frame) plus the fixed celestial pole and the sky's sidereal rotation per frame. Each frame's full pixel-accurate spec comes from calling sky_view at that instant; this tool plans the timeline. Use for sunset-to-night transitions, star-trail planning, or Moon-phase progressions. Endpoint: https://www.ephemengine.com/api/mcp
- synthetic_validate - Check an authored synthetic celestial system for ill-defined inputs: duplicate body ids, non-positive periods, out-of-range eccentricity, or a dangling observer. Returns `impossible` and a list of problems — the same honesty pattern as compileForm. Endpoint: https://www.ephemengine.com/api/mcp
- synthetic_positions - Positions of every body in an authored synthetic system at one instant. Three body modes: `placement` (fixed longitude), `periodic` (uniform motion), `kepler` (constant elements). With `observer` set on the system, positions are geocentric/apparent from that body (outer bodies can show retrograde). Pass `t_days` for abstract day units, or `date` (UT ISO) when body `epoch` values are Julian Days. Returns speed and retrograde per body. Endpoint: https://www.ephemengine.com/api/mcp
- synthetic_sky_view - Sky View for a mix of real and synthetic bodies: register the authored system on an ephemeral engine, then frame the visible sky like sky_view. Synthetic bodies can carry render attributes (sizeDeg, magnitude, color) that flow into the pixel spec and prompt. Real Sun/Moon/planets stay for twilight and context unless omitted from `bodies`. Endpoint: https://www.ephemengine.com/api/mcp
- transits - Transiting planets vs natal chart: aspects within orb (applying/separating), natal house per transiting body. Endpoint: https://www.ephemengine.com/api/mcp
- synastry - Compare two people's birth charts: inter-chart aspects with orbs, house overlays both ways, plus ranked citable fact atoms and a ready `brief` (synastry/composite ids for auditCitations). Each person needs date+lat+lon. House overlays always use Placidus (not configurable here). Endpoint: https://www.ephemengine.com/api/mcp
- find_aspect_dates - Exact dates a transiting body makes an aspect, within a range: to a fixed longitude OR to another transiting body. Provide exactly one of target_lon / target_body. Includes retrograde re-hits. Body names are snake_case (mean_node, true_node). Endpoint: https://www.ephemengine.com/api/mcp
- rectification_grid - Rectification sweep: ASC/MC at each step across a window of UTC hours on one date, with ASC sign-change times. Use when the birth time is unknown and you want candidate times. The sweep runs over window_start_hour..window_end_hour (UTC hours of the given date); the date's time portion is ignored. Endpoint: https://www.ephemengine.com/api/mcp
- sky_events - Sky events in a UTC date range: rise/set/meridian transits (need lat+lon+body), lunar phases (new/quarters/full), solar and lunar eclipses, stations (body turns retrograde/direct; needs body), zodiac degree crossings (needs body + target_lon). Solar eclipses report global circumstances (type, magnitude, gamma) plus the greatest-eclipse location and path width; add lat+lon to also get local circumstances (type seen, magnitude, obscuration, contact times C1-C4). Lunar eclipses report type and magnitude; add lat+lon to learn whether the Moon is above the horizon there. Times to the second vs Swiss Ephemeris (stations to ~1 min: ill-conditioned by nature). Range <= 370 days. Endpoint: https://www.ephemengine.com/api/mcp
- planetary_hours - Planetary hours for a moment and place: the unequal hour in effect (its ruler, day/night, hour number 1-24, start/end UTC), the ruler of the planetary day, and the full 24-hour ruler sequence. Hours split the day (sunrise to sunset) and night (sunset to next sunrise) into twelve each; the day ruler is the weekday ruler and the hours follow the Chaldean order. Needs lat+lon. Returns available:false above the polar circles when the Sun does not rise or set that day. Endpoint: https://www.ephemengine.com/api/mcp
- void_of_course - Void-of-course Moon at a moment: whether the Moon makes no further Ptolemaic aspect to a traditional planet (Sun..Saturn) before it leaves its current sign. Returns the Moon's sign, the UTC time it exits that sign, and the UTC time of its next perfecting aspect (null when none remains -- i.e. void). Tropical by default. Endpoint: https://www.ephemengine.com/api/mcp
- returns - Solar or lunar return: the instant(s) a body returns to its natal longitude within a window, plus the full return chart for the first one. The Sun returns about yearly (the solar-return chart for the year), the Moon about monthly. Return chart is cast for the return moment at return_lat/return_lon (defaults to the birthplace; pass the current/relocated place for a relocated return). Endpoint: https://www.ephemengine.com/api/mcp
- progressions - Secondary progressions (day-for-a-year) and solar-arc directions of a natal chart to a target date. Returns, per body, the secondary-progressed longitude and the solar-arc-directed longitude, plus the solar arc itself. Longitudes only (no houses), so no birthplace is needed. Endpoint: https://www.ephemengine.com/api/mcp
- composite - Relationship charts for two people: the midpoint composite (each body and angle is the shorter-arc midpoint of the two natal positions) and the Davison chart (a real chart cast for the midpoint in time and place). Each person needs date+lat+lon. Endpoint: https://www.ephemengine.com/api/mcp
- dignities - Essential dignity and sect for the seven traditional planets at a moment and place. Per planet: its sign, any essential dignity (domicile/exaltation/detriment/fall), its weighted essential-dignity score (Lilly: rulership 5, exaltation 4, triplicity 3, term 2, face 1; detriment -5, fall -4) with a peregrine flag, its planetary sect (diurnal/nocturnal, null for Mercury), and whether it is in sect given a day or night chart. The chart is day when the Sun is above the horizon — so lat+lon are required. Endpoint: https://www.ephemengine.com/api/mcp
- lots - The seven Hermetic lots (Arabic parts) — Fortune, Spirit, Eros, Necessity, Courage, Victory, Nemesis — cast from the Ascendant and reversing direction by sect (a chart is day when the Sun is above the horizon). Per lot: its longitude and zodiacal position. Lots are anchored to the Ascendant, so an exact time and lat+lon are required. Fortune and Spirit are mirror images about the Ascendant. Tropical by default. Endpoint: https://www.ephemengine.com/api/mcp
- profections - Annual and monthly profections (a Hellenistic time-lord technique) at a target date. The natal Ascendant advances one whole sign per year of life; the profected sign's traditional ruler is the lord of the year, the single most important time-lord for that year. Returns the age in years, the month within the profection year, and the annual and monthly profected sign (with its whole-sign house from the natal Ascendant and its lord). Needs the birth time and place for the Ascendant. Endpoint: https://www.ephemengine.com/api/mcp
- firdaria - Firdaria (firdariyyat): the Persian/medieval planetary time-lord periods. Life divides into nine major periods totalling 75 years — the seven planets (a day chart starts with the Sun, a night chart with the Moon) then the North and South Nodes — each planetary period split into seven sub-periods. Returns the full timeline (each period and sub-period with UTC start/end) and, when target_date is given, the major and sub lord active then. Sect is taken from the birth chart, so lat+lon are required; pure time arithmetic, no zodiac. Endpoint: https://www.ephemengine.com/api/mcp
- releasing - Zodiacal releasing (aphesis), the Hellenistic time-lord technique from Vettius Valens, released from a Lot (Spirit by default, or Fortune). From the Lot's sign, periods release sign by sign with planetary minor-year lengths on the 360-day-year convention; each level is a twelfth of the one above (L1..L4), and a loop back to the starting sign looses the bond, jumping once to the opposite sign (+6). Returns the timeline down to max_level over the horizon and, when target_date is given, the L1..L4 lords active then. Anchored to the natal Lot, so an exact time and lat+lon are required. Endpoint: https://www.ephemengine.com/api/mcp
- directions - Primary (mundane) directions of the seven traditional planets to the four angles (MC, IC, Ascendant, Descendant), and optionally between the planets themselves. The diurnal rotation carries a body to the angle (or a promissor to a significator); the arc of rotation, converted by a time key (Naibod 0.9856473°/yr by default, or Ptolemy 1°/yr), gives the age of the direction. Returns the directions within max_years, sorted by age, each with its arc, age in years, and UTC date. With include_mundane, also returns the planet-to-planet (promissor → significator) directions. Circumpolar bodies have no Ascendant/Descendant directions. Needs the birth time and place; equatorial, so zodiac is irrelevant. Endpoint: https://www.ephemengine.com/api/mcp
- nakshatras - The nakshatra (one of the 27 lunar mansions of 13°20′) of each classical point on the sidereal zodiac: the seven traditional planets and the Ascendant (lagna). Per point: the nakshatra name, its pada (quarter, 1–4), the ruling planet (the Vimshottari lord), and degrees into the nakshatra. The Moon's nakshatra (janma nakshatra) anchors the Vimshottari dasha. Sidereal by definition; Lahiri ayanamsa by default. Needs the birth time and place for the Ascendant. Endpoint: https://www.ephemengine.com/api/mcp
- dasha - Vedic dasha periods — planetary time-lord cycles started from the Moon's birth nakshatra. system selects Vimshottari (120-year, the standard), Yogini (36-year, eight yoginis), or Ashtottari (108-year). Returns the period timeline (mahadasha → antardasha) with UTC start/end, the balance of the first period at birth, and — when target_date is given — the lords active then (Vimshottari also gives the pratyantardasha). Sidereal; Lahiri by default. Needs the birth time and place. Endpoint: https://www.ephemengine.com/api/mcp
- vargas - Parashari divisional charts (vargas): the sign of each of the seven planets and the Ascendant in the requested D-charts — D1 rasi, D2 hora, D3 drekkana, D9 navamsa, D10 dasamsa, D12 dwadasamsa, D30 trimsamsa. Per point in each chart: the divisional sign and the division number within the rasi. The navamsa (D9) is the most consulted after the rasi. Sidereal; Lahiri by default. Needs the birth time and place for the Ascendant. Endpoint: https://www.ephemengine.com/api/mcp
- yogas - Vedic yogas (planetary combinations) on the sidereal rasi chart: the five Pancha Mahapurusha yogas (Ruchaka, Bhadra, Hamsa, Malavya, Shasha), Gajakesari, Budha-Aditya, and Chandra-Mangala; whether Kemadruma (the isolated-Moon yoga) is present; the raja yogas (a kendra lord associating with a trikona lord) and dhana (wealth) yogas, each as the lord pair and how they associate (conjunction, aspect, or exchange); and the chart's yogakarakas (a planet ruling both a kendra and a trikona). Sidereal; Lahiri by default. Needs the birth time and place. Endpoint: https://www.ephemengine.com/api/mcp
- aspect_patterns - Classical aspect configurations in a chart: T-squares, grand trines, grand crosses, yods, kites, mystic rectangles, and stelliums by sign and by house. Each is a structured object with the participating bodies and the worst defining-aspect orb; T-squares and yods also name the apex, stelliums their sign or house. Reported patterns are maximal — a grand cross hides the T-squares it contains, a kite its grand trine. Pure geometry (engine orbs plus a quincunx for yods), no interpretation. Needs date, lat, lon. Endpoint: https://www.ephemengine.com/api/mcp
- chart_signature - A chart's structural signature as plain counts: element, modality, angularity, quadrant, and hemisphere distributions over the bodies; the dominant element, modality, and most-occupied sign; and the classical chart ruler (the ruler of the Ascendant's sign). Counts only, no interpretation — a compact summary for emphasis and comparison. Needs date, lat, lon. Endpoint: https://www.ephemengine.com/api/mcp
- chart_facts - A chart's validated facts as ranked, citable atoms for interpretation. Each fact has a stable id (e.g. "aspect:moon~neptune:conjunction"), the bodies it concerns, a salience score (luminaries, angular placements, the chart ruler, tight/hard aspects, configurations rank high), and a plain-language statement. Facts span placements, aspects, configurations, the structural signature, dispositors and receptions, a body's tight conjunction with a bright fixed star (e.g. "star:jupiter:Sirius"), and the Part of Fortune and Spirit (e.g. "lot:fortune"). Read the facts, write the interpretation in your own words, and cite the [id] each statement rests on — do not introduce facts not listed. Returns the ranked facts plus a ready-to-interpret `brief`.

By default a real birth chart: pass date+lat+lon. The chart's grounding is first-class via `realm` (what it is: observed/forecast/fictional/mythic/archetypal/…) and the time: an exact `date`, an uncertain `earliest`+`latest` range (the brief then frames it as provisional and trusts the Moon/angles/houses less), `constraints` for an archetypal chart with no time (synthesized via the compiler), or a full structured `when` (relative-to-another-event or a narrative calendar). A `when` of kind `relative` looks its `anchorId` up in `anchors` (a map of id → UTC instant supplied in the request). Omit lat+lon for a placeless chart (nominal houses). Endpoint: https://www.ephemengine.com/api/mcp
- counterfactual_chart - A birth chart, perturbed — a 'what if'. Give a base chart (date+lat+lon) and an edit: `shift_time` (e.g. '1h', '-30m', 'P1D') moves the instant ("born an hour later"), `move_lat`+`move_lon` recompute at another place, and/or `set_longitudes` moves bodies to new ecliptic degrees ("Mars in the next sign"). Returns the diff vs the original: bodies that changed sign or house, aspects gained or lost, and angles that changed sign. A time/place edit rotates the houses and angles while planets stay put; a longitude splice moves only those bodies and recomputes their aspects. Endpoint: https://www.ephemengine.com/api/mcp
- similar_skies - Find when the sky most resembled a reference moment. Builds a feature vector for the reference date's planetary configuration and scans a window for the closest matches by cosine similarity (1.0 = identical configuration). Answers 'when did the sky last look like this?' for transit echoes and historical analogues. Returns the top matches with their similarity, highest first. Endpoint: https://www.ephemengine.com/api/mcp
- electional_search - Rank moments in a window for an electional aim. Samples the window and scores each instant by how closely a set of wanted body-to-body aspects is satisfied (tighter and applying aspects score higher), optionally penalizing a void-of-course Moon. Returns the top moments with the aspects that matched. Body-to-body only; for aspects to the angles, compute the chart at a candidate moment. Endpoint: https://www.ephemengine.com/api/mcp
- cosmic_weather - The mundane sky on a date: the active aspect configurations among the transiting planets (T-squares, grand trines, grand crosses, yods, kites, mystic rectangles, stelliums by sign), any planet stationing within a window, and whether the Moon is void of course. A 'cosmic weather' snapshot; no birth chart or location needed. Endpoint: https://www.ephemengine.com/api/mcp

## Resources
- ui://widget/chart.html - Chart wheel Renders the natal_chart / current_sky payload as a caelus-wheel chart. MIME type: text/html;profile=mcp-app
- caelus://accuracy - Validation table Per-body accuracy: vs Swiss Ephemeris (swiss) and JPL Horizons apparent positions (jpl). MIME type: application/json
- caelus://glossary - Glossary Machine-readable definitions: aspect angles and default orbs, signs, bodies, the twelve house systems, and essential dignities (domicile/exaltation/detriment/fall). MIME type: application/json

## Prompts
- rectification_session - Birth-time rectification Guide a birth-time rectification: sweep candidate ascendants across the day, then test them against dated life events. Arguments: date, lat, lon, events

## Metadata
- Owner: io.github.heavyblotto
- Version: 0.23.0
- Runtime: Npm
- Transports: STDIO, HTTP
- License: Not captured
- Language: Not captured
- Stars: Not captured
- Updated: Jun 21, 2026
- Source: https://registry.modelcontextprotocol.io