You join a team and inherit a service with no documentation and the original author has left. Walk me through your first week.
What they are really testing: They want to see whether you have a systematic way of building a map of unknown code, or whether you will freeze and wait for someone to explain it to you. They are also testing whether you will break production while exploring.
A real interview question
You join a team and inherit a service with no documentation and the original author has left. Walk me through your first week.
What most people say
drag me
“I would read through all the code carefully from top to bottom until I understood the whole thing, and then I would start making changes.”
Reading everything is not a plan, it does not scale past a few thousand lines, and it shows no sense of priority, risk or how to build a mental model from the outside in.
The follow-ups they ask next
How did you avoid breaking things while exploring?
Talk about read only access first, running against copies of data, and never running a write path in prod to learn.
What if the code was too big to map in a week?
Say you would map only the path your task touches, and leave the rest as a labelled unknown rather than pretending to know it.
What the interviewer is listening for
- Starts from entry points, config, alerts and logs rather than line by line reading
- Produces written artefacts that outlive the exploration
- Explicitly tracks what they do not yet understand
- Ships a small verified change early instead of a big risky one
What sinks the answer
- Plans to read the whole codebase before doing anything
- Experiments directly in production to see what happens
- Waits to be told rather than going and finding out
- No output at the end of the week
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“I have not inherited an orphaned service yet, but here is how I would attack it: I would learn it from the outside in, config and alerts and logs first, and write down every question I could not answer. Concretely, on day one I would ...”
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