EOP API documentation

Access

The data is free. We distinguish browsing from programmatic access.

The source data stays public. The key applies to our service only, not to the data itself. The original file is in the public domain and anyone may fetch it straight from USNO, with no account and no involvement from us.

What the key gives you

• queries for single epochs, date ranges and the last N days,
• the full series back to 1973 — the static files cover only the last ~10 years,
• linear interpolation for fractional MJD (e.g. mjd=61250.5),
• responses in JSON and CSV,
• a default limit of 1000 requests per day (negotiable if you need more),
• during the trial phase — no charge; chargeable later.

Authentication

Pass the key in the X-API-Key header:

curl -H "X-API-Key: gd_twoj_klucz" \
     "https://gnss.day/api/v1/eop?last=1"

The key identifies you to the service — treat it like a password. Keep it out of published repositories and out of URLs that end up in logs.

Sample response

This is what the API returns. Below, a real response for epoch 2026-07-30.

JSON — a single epoch

$ curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?date=2026-07-30"

{
  "count": 1,
  "data": [
    {
      "mjd":  61251,
      "date": "2026-07-30",
      "type": "final/rapid",
      "eop": {
        "xp_arcsec": 0.219628,
        "yp_arcsec": 0.365836,
        "ut1_utc_s": 0.0129614,
        "lod_ms":    null,
        "dX_mas":    -0.011,
        "dY_mas":    -0.028
      },
      "sigma": {
        "xp_arcsec": 9e-05,
        "yp_arcsec": 9e-05,
        "ut1_utc_s": 9.5e-06,
        "lod_ms":    null
      }
    }
  ]
}

CSV — the same range as CSV

$ curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?last=2&format=csv"

mjd,date,type,xp_arcsec,yp_arcsec,ut1_utc_s,lod_ms,dX_mas,dY_mas,sig_xp,sig_yp,sig_ut1,sig_lod
61250,2026-07-29,final/rapid,0.219198,0.366419,0.0126808,-0.4121,-0.002,-0.04,9.1e-05,9e-05,1.37e-05,0.0094
61251,2026-07-30,final/rapid,0.219628,0.365836,0.0129614,,-0.011,-0.028,9e-05,9e-05,9.5e-06,

Poster (PNG, 1600×4150) →

Full field and unit reference →

What the API serves

Six Earth orientation parameters with their uncertainties, split into observations and predictions.

Observations versus predictions

Every record carries a type flag. The distinction matters — predictions have an order of magnitude more uncertainty and change with each new release.

Field reference

Units follow IERS conventions. Fields may be null when the source publishes no value for that epoch.

Endpoints

Available now no key

The portal serves the data as static files. They are public and usable today, programmatically included — no registration.

Queries key required

The query endpoints are live. Authenticate with the X-API-Key header. They cover the full series back to 1973 — more than the static files, which are trimmed to the last ~10 years.

The &format=json|csv parameter switches the response format. Authenticate with X-API-Key: <key>.

Examples

Working today, against the static files — no account, no key.

Fetching the metadata

curl -s https://gnss.day/data/eop_meta.json

Latest observed epoch (Python)

# Columnar format: the i-th index of every array is the same epoch
import json, urllib.request

B = "https://gnss.day/data/"
d = json.load(urllib.request.urlopen(B + "eop.json"))
m = json.load(urllib.request.urlopen(B + "eop_meta.json"))

i = d["mjd"].index(m["last_obs_mjd"])
print(m["last_obs_date"],
      "xp=", d["xp"][i],
      "yp=", d["yp"][i],
      "UT1-UTC=", d["ut1"][i])

Filtering observations only

# flag is a compact string, one character per epoch: "IIII...PPP"
obs = [(d["mjd"][i], d["xp"][i])
       for i, f in enumerate(d["flag"]) if f == "I"]
print(len(obs), "observations")

Response structure (excerpt)

{
  "mjd":  [61249, 61250, 61251],
  "flag": "III",
  "xp":   [0.218763, 0.219198, 0.219628],
  "yp":   [0.367005, 0.366419, 0.365836],
  "ut1":  [0.0124, 0.0126808, 0.0129614],
  "lod":  [-0.3987, -0.4121, null]   // null = absent from the source
}

API queries (with a key)

# a single epoch
curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?date=2026-07-30"

# the last 30 observed days, as CSV
curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?last=30&format=csv"

# a date range
curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?start=2026-01-01&end=2026-06-30"

# interpolated to UTC noon (fractional MJD)
curl -H "X-API-Key: $KEY" \
     "https://gnss.day/api/v1/eop?mjd=61250.5"

A Python client

import json, urllib.request

def eop(**q):
    """Query the EOP API. Requires the key in KEY."""
    url = "https://gnss.day/api/v1/eop?" + urllib.parse.urlencode(q)
    req = urllib.request.Request(url, headers={"X-API-Key": KEY})
    with urllib.request.urlopen(req) as r:
        return json.load(r)

d = eop(last=7)
for r in d["data"]:
    print(r["date"], r["eop"]["xp_arcsec"], r["eop"]["ut1_utc_s"])

Licence and terms of use

The data

Sourced from the USNO / IERS Rapid Service–Prediction Center and carrying the statement “Approved for public release: distribution unlimited” — as a work of the US government (17 U.S.C. § 105) it is in the public domain. We add no licence restrictions of our own: use it freely, commercially included.

Attribution is not legally required, but please cite the source — it is standard scientific practice and helps your readers verify the data.

Disclaimers

• No warranty. The data is served exactly as we receive it from the source. We guarantee neither accuracy, nor completeness, nor continuity of service.
• An independent service. gnss.day is not affiliated with USNO, IERS, NASA or ESA and does not act on their behalf. Naming the data source does not imply their endorsement of this service.
• Safety-critical use. For navigation, safety or any other high-stakes application, go to the source directly and verify the data.

Personal data

Browsing the portal needs no account and involves no collection of personal data. Requesting an API key requires only an email address — processed to provide the service (Art. 6(1)(b) GDPR). We pass it to no one and use it for no marketing. The key can be revoked and the contact details deleted at any time — just write to kontakt@gdansk.ai.

Use of the service is governed by the terms of service (Polish). A detailed analysis of the source licensing is kept in the project documentation and is available on request at the contact address.