Tides API — FES2022 tide predictions

The Tides API predicts astronomical tide heights for any coastal or offshore point on Earth — no tide-station lookup, no "nearest station 40 km away". Predictions are computed from FES2022, the latest generation of the CNES/LEGOS/NOVELTIS/CLS global tide atlas (34 constituents on a 1/30° grid, assimilating three decades of altimetry), distributed by AVISO.

Because it is a model, any date works: past reconstruction and far-future planning cost the same one call.

Endpoint auth: API key (Authorization: Bearer tt_live_…)

Postman: a fully documented collection covering every thirdtrail API lives in the repo at docs/postman/ — import the collection + environment, set apiKey, and go.

GET /v1/tides/heights/

Water-height time series relative to mean sea level.

Param	Required	Notes
`lat`, `lon`	yes	decimal degrees
`start_date`	no	`YYYY-MM-DD`, default today (UTC). Past dates need a paid plan
`days`	no	window length; plan-capped
`step`	no	`1m 5m 10m 15m 30m 1h`, default `10m`; finest step is plan-gated
`datum`	no	`msl` (default) or `lat` (Lowest Astronomical Tide, Pro+)
`tz` / `utc_offset` / `auto_timezone`	no	output timezone

curl -H "Authorization: Bearer tt_live_…" \
  "https://thirdtrail.life/v1/tides/heights/?lat=48.383&lon=-4.495&days=2&step=30m"

{
  "resolved": {"model": "FES2022B", "timezone": "UTC", "datum": "MSL"},
  "heights": [
    {"time": "2026-07-25T00:00:00+00:00", "height_m": -1.891},
    {"time": "2026-07-25T00:30:00+00:00", "height_m": -1.634}
  ]
}

GET /v1/tides/extremes/

High and low waters (times + heights), parabolic-refined to seconds. Same parameters as /heights/ minus step.

GET /v1/tides/window/ (Starter+)

The coastal planning call: for each day, tide extremes plus sunrise, sunset, twilight, golden/blue hour and moon phase from our ephemerides engine — one request instead of two products. Built for photographers, anglers, drone pilots and shore crews.

Same parameters as /extremes/, plus:

Param	Required	Notes
`elevation`	no	metres above sea level, −500 to 9000. Applies to the sun and moon only
`auto_elevation`	no	derive it from `lat` / `lon` (Pro+)

Elevation matters here for the same reason it matters everywhere else in thirdtrail: the higher you stand, the earlier the sun clears the horizon. On top of a 214 m sea cliff sunrise is about three minutes earlier than at the water's edge, and every golden- and blue-hour boundary moves with it — a meaningful slice of a window that is only 20–40 minutes long.

Tide heights are not affected. How high the observer stands has no bearing on the ocean surface, which is why /heights/ and /extremes/ take no elevation parameter at all rather than accepting one and ignoring it. resolved.elevation_m and resolved.elevation_source (user, auto or default) report what was actually applied.

GET /v1/tides/constituents/ (Pro+)

The 34 harmonic constants (amplitude, Greenwich phase lag, angular speed) interpolated at your point — compute offline, verify our numbers, or feed your own synthesis.

POST /v1/tides/bulk/ (Pro+)

{"queries": [{"lat": …, "lon": …, "days": …}, …]} → extremes for up to 100 (Pro) / 1,000 (Business) locations per request.

Datums

Heights default to MSL. datum=lat (Pro+) re-references to Lowest Astronomical Tide computed from a full 18.6-year nodal scan at your exact point, and the response carries LAT/HAT/MHWS/MLWS offsets so you can re-reference to chart datum yourself.

Accuracy & limitations

Astronomical tide only — no meteorological surge, no river discharge.
FES2022 vs FES2014: markedly better coastal accuracy (finer mesh, better bathymetry, more assimilation data). Open-ocean accuracy ~1 cm RMS; complex shelf areas remain harder for any global model.
Our synthesis engine is validated constituent-by-constituent against CNES's own pyfes reference (equilibrium arguments to <0.2°, nodal factors to <0.3%).
Not for navigation. See our safety page.

FES2022 was produced by LEGOS, NOVELTIS and CLS, funded by CNES, and is distributed by AVISO.