Some companies will choose to do a technical phone screen before bringing you on-site or giving you any sort of technical challenge
This phone call will generally be with a senior developer, lead developer, or engineering manager of some sort. Expect the call to be very technical in nature, and be prepared to speak in great detail and depth about your work history, projects, and general trivia like “how does the Internet work” or “explain the time complexity of a binary search”.
Some companies will use online coding tools for their technical screen. When I interviewed at Google in the past, we used a shared Google Doc for me to write code. There are far more sophisticated tools for this, of course, but there’s no code-completion or hints/linters in Google Docs, so it was a true test that I could write code on my own.
The most important thing in this call is to be as accurate and honest as you can. Never guess at answers; instead, tell them you don’t know the answer but that you’d like to offer an idea if that’s alright. They may move on to a different question. Interviewers can tell very easily when you’re making things up, or that you’re guessing at answers.
Their job here is to determine the depth of your technical knowledge in several areas to see if you have the necessary skills to fill a gap/need on their team.
Always ask how deep they would like you to get on your answers. For example, “how does the internet work” could be a simple answer at high level, but could get into some very complex topics of routers and DNS, TCP vs UDP packets, etc..