Free APIs — liturgical calendar

Every API on this page is free, without a key, without an account, with open CORS: callable from a browser, a server or a mobile app. Responses are CDN-cached for one hour.

Base URL

https://categpt.chat

The feast of the day — GET /api/v1/feast

Returns the full liturgical day: both forms of the rite, their texts and the biblical reference of every text. Days close to today are generated on the fly when missing.

curl "https://categpt.chat/api/v1/feast?locale=en"

curl "https://categpt.chat/api/v1/feast?date=2026-07-29&locale=fr"

At the top level, only date and sameFeast — plus credits (the sources). Everything else lives in nom and vom, which carry exactly the same keys:

{
  "date": "2026-07-25",
  "sameFeast": false,
  "nom": {
    "name": "St Mary Magdalene",
    "rank": "Feast",
    "rawRank": "Fête",
    "latinName": null,
    "color": "blanc",
    "line": "Saturday, week 16 in Ordinary Time — Year II",
    "commemorations": [],
    "commemorationLine": null,
    "description": "…Markdown description…",
    "excerpt": "…two-sentence summary…",
    "permalink": "https://app.categpt.chat/en/saint/july-25-2026-st-mary-magdalene",
    "slug": "july-25-2026-st-mary-magdalene",
    "questions": ["…", "…", "…"],
    "mass": [
      { "key": "first_reading", "label": "First reading", "ref": "Ct 3, 1-4a", "text": "<p>…</p>", "source": { "language": "fr", "label": "Première lecture", "ref": "Ct 3, 1-4a", "text": "<p>…</p>" } },
      { "key": "second_reading", "label": "Second reading", "ref": "1 Co 13, 1-13", "text": "<p>…</p>", "source": { "language": "fr", "label": "Deuxième lecture", "ref": "1 Co 13, 1-13", "text": "<p>…</p>" } },
      { "key": "gospel", "label": "Gospel", "ref": "Jn 20, 1-2.11-18", "text": "<p>…</p>", "source": { "language": "fr", "label": "Évangile", "ref": "Jn 20, 1-2.11-18", "text": "<p>…</p>" } }
    ],
    "offices": {
      "lauds": [
        { "key": "hymn", "label": "Hymne", "ref": null, "text": "<p>…</p>", "source": null },
        { "key": "short_reading", "label": "Parole de Dieu", "ref": "Rm 8, 26-27", "text": "<p>…</p>", "source": null }
      ],
      "vespers": [ { "key": "short_reading", "label": "Parole de Dieu", "ref": "…", "text": "<p>…</p>", "source": null } ]
    },
    "localPropers": [ { "zone": "france", "name": "Sts Martha, Mary and Lazarus" } ],
    "localPropersLine": "France: Sts Martha, Mary and Lazarus"
  },
  "vom": {
    "name": "St Christopher, Martyr",
    "rank": "3rd class",
    "rawRank": "III. classis",
    "latinName": "S. Christophori Martyris",
    "color": "rouge",
    "line": "Saturday after the 8th Sunday after Pentecost",
    "commemorations": ["St Christopher, Martyr"],
    "commemorationLine": "Commemoration of St Christopher, Martyr",
    "description": "…description of the Vetus Ordo feast itself…",
    "excerpt": "…two-sentence summary…",
    "permalink": "https://app.categpt.chat/en/saint/july-25-2026-st-christopher-martyr",
    "slug": "july-25-2026-st-christopher-martyr",
    "questions": ["…", "…", "…"],
    "mass": [
      { "key": "introit", "label": "Introit", "ref": "Ps 138:17", "text": "<p>…</p>", "source": { "language": "la", "label": "Introitus", "ref": "Ps 138:17", "text": "<p>…</p>" } },
      { "key": "collect", "label": "Collect", "ref": null, "text": "<p>…</p>", "source": { "language": "la", "label": "Oratio", "ref": null, "text": "<p>…</p>" } },
      { "key": "communion", "label": "Communion", "ref": "Ps 33:9", "text": "<p>…</p>", "source": { "language": "la", "label": "Communio", "ref": "Ps 33:9", "text": "<p>…</p>" } }
    ],
    "offices": {
      "sext": [
        { "key": "short_reading", "label": "Little Chapter", "ref": "Gal 6:2", "text": "<p>…</p>", "source": { "language": "la", "label": "Capitulum Responsorium Versus", "ref": "Gal 6:2", "text": "<p>…</p>" } },
        { "key": "collect", "label": "Collect", "ref": null, "text": "<p>…</p>", "source": { "language": "la", "label": "Oratio", "ref": null, "text": "<p>…</p>" } }
      ]
    },
    "localPropers": [],
    "localPropersLine": null
  },
  "credits": {
    "nom": { "source": "AELF", "url": "https://www.aelf.org" },
    "vom": { "source": "Divinum Officium", "url": "https://www.divinumofficium.com/" }
  }
}

Strict NOM / VOM equality

nom carries the celebration of the current Roman calendar (Novus Ordo, AELF texts), vom the one of the Vetus Ordo Missae (1962 calendar, Divinum Officium texts). Both blocks have the same key set — no field exists on one side only:

sameFeast is true when both calendars celebrate the same feast that day, false when they differ, null when the day has no VOM data — vom is then null.

It is information, never a conditional to write: description, excerpt and questions always belong to their own block's ordo, whatever its value. A block whose text has not been produced yet carries null — it never borrows the other ordo's. Two different feasts give two different permalinks. Returns 404 (not_found) when no data exists for that day.

Liturgical texts and biblical references

mass and each hour of offices are lists of identical objects on both ordos:

One vocabulary, in English, for both ordos

Every key is English, and the two ordos share a key whenever they mean the same thing. That is what makes the two blocks interchangeable: swapping vom for nom in a path gives the same result, for everything the two calendars have in common.

Hours — matins, lauds, prime, terce, sext, none, vespers, compline. Each ordo serves only the ones it has: the Novus Ordo has no prime, and its office of readings is matins.

Mass — shared: epistle, gospel, sequence, psalm, canticle, reading. Novus Ordo only: first_reading, second_reading, third_reading, gospel_acclamation. Vetus Ordo only: introit, collect, gradual, alleluia, tract, offertory, secret, communion, postcommunion, commemoration.

The mass decides what its readings are called: a mass with a single reading before the gospel — the ordinary weekday — serves it as reading, "Reading", not as first_reading; first_reading and second_reading come as a pair, as they do in the missal. And the short form of the gospel, which AELF publishes on some Sundays alongside the full text, is not served: the mass holds the full gospel only.

Offices — shared: hymn, antiphon, psalm, short_reading (AELF's "péricope" and Divinum Officium's "capitulum" are the same object), responsory, versicle, collect, reading, te_deum. Novus Ordo only: introduction, patristic_reading, patristic_responsory, psalm_versicle, intercession, our_father, blessing, invitatory_antiphon, invitatory_psalm, benedictus, magnificat, nunc_dimittis and their antiphons. Vetus Ordo only: lesson_1…lesson_9, the Matins lessons.

Numbered parts keep their number (psalm_2, antiphon_3), and a key repeated inside the same list is suffixed _2, _3…

Zone codes (france, belgique…) are values published by AELF, not keys: they are served as-is, so they stay comparable with the source.

Everything is therefore retrieved by key, without knowing anything about the sources’ formats:

const day = await fetch(`https://categpt.chat/api/v1/feast?date=2026-07-25`).then(r => r.json());

// The reference of the little chapter of Sext in the Vetus Ordo → "Gal 6:2"
day.vom.offices.sext.find(t => t.key === 'short_reading').ref;

// The 2nd reading of a Novus Ordo Sunday → "1 Co 13, 1-13"
day.nom.mass.find(t => t.key === 'second_reading').ref;

// The communion antiphon of a Vetus Ordo day → "Ps 33:9"
day.vom.mass.find(t => t.key === 'communion').ref;

Novus Ordo references come from AELF’s own ref field; Vetus Ordo ones are parsed out of the text itself (Divinum Officium prints them as a rubric, on their own line or at the end of a reading incipit) using a list of Latin and vernacular book abbreviations — ref is null when no reference is recognised.

description, excerpt, name, rank, line, commemorations and the labels come back in the requested locale (French fallback, then Latin on the VOM side). Novus Ordo mass texts are translated when locale ≠ fr; Novus Ordo offices stay in French (official AELF text). credits gives the source to display next to each ordo’s texts.

The liturgical day — GET /api/liturgical/{date}

The same payload as /api/v1/feast, plus prev / next navigation — this is the API the site itself consumes for its daily pages.

curl "https://categpt.chat/api/liturgical/2026-07-29?locale=en"

curl "https://categpt.chat/api/liturgical/2026-07-29?locale=fr"

prev and next are null when the adjacent day is not stored yet; otherwise:

The calendar — GET /api/liturgical/calendar

One month of entries ready to list — what the liturgical calendar page shows. Read-only: a day missing from the database simply yields one entry fewer.

curl "https://categpt.chat/api/liturgical/calendar?month=2026-07&locale=en"

curl "https://categpt.chat/api/liturgical/calendar?month=2026-07&locale=fr"

Each entry of entries:

The card of the day — GET /api/liturgical/card/{date}

A 1080 × 1080 JPEG of the day (feast name, liturgical colour), freely embeddable — the visual of the project's daily posts. Stored days only.

<img src="https://categpt.chat/api/liturgical/card/2026-07-29" alt="Feast of the day" width="540">

curl "https://categpt.chat/api/liturgical/card/2026-07-29"

The RSS feeds — GET /api/feed/feast-of-the-day

Two RSS 2.0 feeds of the saint of the day (French), one per form of the rite: the last 30 days, each item linking to its permanent page, with the name, link and excerpt of its own ordo.

https://categpt.chat/api/feed/feast-of-the-day
https://categpt.chat/api/feed/feast-of-the-day?ordo=vom

Both feeds are advertised in the <head> of every public page (<link rel="alternate" type="application/rss+xml">): an RSS reader pointed at categpt.chat discovers them by itself.

curl "https://categpt.chat/api/feed/feast-of-the-day?ordo=nom"

Errors

The /api/v1/* endpoints answer { "error": { "code": "…" } }; the /api/liturgical/* endpoints answer { "error": "…" }:

OpenAPI specification

The whole API — free and keyed — is described by an OpenAPI 3.1 specification generated from the same source as this page:

https://categpt.chat/api/openapi

Import it into Postman, Insomnia or a client generator to get typed requests and schemas.

Go further

• Keyed API — sourced answers
• Widget & embeddable card
• Contact: info@categpt.chat