Did the MongoDB virtual onsite in March. Here's a straightforward breakdown of how it actually goes, because the prep advice floating around is mostly generic and misses some MongoDB-specific things.
Format. All virtual now. 5 rounds across roughly two days (they may compress to one day depending on interviewer schedules). You get a Zoom link for each session. Excalidraw or CoderPad depending on the round.
Round 1: Live coding. 60 minutes, one interviewer. Two problems, easier to harder. They start conversationally, almost like they want you to relax. Don't be fooled. The second problem is hard. I got a string manipulation problem and then a graph connectivity problem. Interviewer was engaged but mostly quiet. They'll ask you to explain your approach before coding. Don't skip that step.
Round 2: System design. (See my other post on this. CDC pipeline or equivalent, 60 mins.)
Round 3: Behavioral 1. 45 minutes, focused on collaboration, conflict, and team influence. Questions about a time you had to influence without authority, a time a project went sideways, and one about giving hard feedback to a peer. Standard STAR format but they dig on specifics. They asked follow-up questions after every answer.
Round 4: Behavioral 2. Another 45 minutes, different interviewer. Focused more on technical decision-making and learning. Questions about a time you were wrong, a time you made a call under ambiguity, and one about how you stay current technically.
Round 5: Hiring manager conversation. 30-45 minutes. More informal. They walk you through the team's mission, current projects, and then ask about your career goals. This is also where I got the one curveball: "What's a technology you've changed your opinion on?" Have an honest answer ready.
Total time from onsite to offer was about 12 business days for me. YMMV based on team and volume.
One real piece of advice: don't underestimate the behavioral rounds. I've seen people nail system design and coding and then get dinged on behavioral. MongoDB cares a lot about how you work with people, not just how you code.