Julian Date Converter API

Convert between calendar dates (UTC), Julian Date (JD), Modified Julian Date (MJD) and ordinal dates (YYDDD / YYYYDDD).

POST /api/v1/tools/julian-date-converterMCP julian_date_converterTime & Date

Convert a UTC date and time to a Julian Date, Julian Day Number and Modified Julian Date, or to an ordinal YYDDD date, and convert any of them back.

Input

Send these as a JSON object. Unknown fields are rejected.

from: What the input is: calendar (YYYY-MM-DD date plus optional time), jd, mjd or ordinal (YYDDD or YYYYDDD). (string, one of calendar, jd, mjd, ordinal, required)
value: The input: "2026-10-20" for calendar, "2451545.0" for jd, "51544.5" for mjd, "26293" or "2026293" for ordinal. (string, up to 40 characters, required)
time: calendar only: UTC time as HH:MM or HH:MM:SS. Defaults to midnight. (string, up to 8 characters)

Try it in the browser JSON Schema Get an API key

curl https://pithlab.com/api/v1/tools/julian-date-converter \n  -H "Authorization: Bearer $PITHLAB_KEY" \n  -H "Content-Type: application/json" \n  -d '{"from":"calendar","value":"2000-01-01","time":"12:00"}'

Example response

{
  "ok": true,
  "result": {
    "iso": "2000-01-01",
    "time": "12:00:00",
    "jd": "2451545",
    "mjd": "51544.5",
    "jdn": 2451545,
    "dayOfYear": 1,
    "yyddd": "00001",
    "yyyyddd": "2000001",
    "note": null,
    "text": "2000-01-01 12:00:00 UTC = JD 2451545, MJD 51544.5, ordinal 2000001 (00001)"
  }
}