[fowlerpower]

I think a senior engineer has to know a few things.

They have to have the basics we all need as engineers simply to pass the interview process. The data structures and algorithms, Big O and be able to walk through systems they have worked on in the past and the trade offs they made and why.

Then on top of the basics I look for a few more things. Usually the understanding of multi threading, multi process, asynchronous programming is very different between junior and senior folks. I dive into distributed systems and see if they have any exposure. I dive into multi paradigms and how deep their knowledge is in their respective toolset they have listed on their resume.

I don't necessarily think you need to know multi threading in and out, or distributed systems in and out, or your tool set in and out. You certainly need to know one or two of those though. You need to have some body of work you can speak very well to, this is a huge indicator of seniority. Mentorship and all the other things that go with that help differentiate as well between junior and senior.

I don't think there is a hard rule anywhere. Different folks will look for different things and at least where I work those things I listed are very important differentiators.