API coordinate reference system?

I’m having trouble confirming what CRS the API calls use when lat/lon are supplied and/or returned. Is it EPSG:3857? Thanks for your help!

I believe it is WGS84 (EPSG:4326) as that is what OpenStreetMap uses (the source of our data). This page gives some info about how the 4326 and 3857 are used in APIs and maps:

Thanks @adam! The stackexchange post you linked to highlights my confusion when it says:

All of this further confused by that fact that often even though the map is in Web Mercator(EPSG: 3857), the actual coordinates used are in lat-long (EPSG: 4326). This convention is used in many places, such as:

  • In Most Mapping API,s You can give the coordinates in Lat-long, and the API automatically transforms it to the appropriate Web Mercator coordinates.

So is it fair to say that the inputs and outputs of the OpenRouteService API are in 4326 but transformation to 3857 is likely happening behind the scenes? I was getting confused because I’ve seen several sources state that map web services are usually based in 3857 and wasn’t sure if I needed to do the transformation myself…

Input and output is 4326, internally different projections are used depending on the usecase (e.g. mollweide for area calcualtion).
Our code is opensource so you can also take a look inside to see what projections are used.