Is there a source with records of the participants and/or casualties of the Russian army during the WWI period (1914-1918) and thereabouts? Preferably on-line and indexed/searchable by name(s), birthplace, place of residence and whatever else data the authorities gathered for the recruits.
There are some sources but they are fragmented and most of them are not digitized yet.
One online source about WWI casualties for 1914-1915 years is in the Russian State Library. It's far from being complete, but it's the largest online source I know of.
I don't think there are any indexed/searchable sources at all.
There is a Russian website that has a project going to provide the data within pdf format spreadsheets. These are also in Russian and provided according to Russian province. You can find these records at http://svrt.ru/1914/1914-1.htm .
I've had simliar questions about those records (and those of WWII). For WWI I was directed to try https://gwar.mil.ru/