When I'm hiring a senior engineer, the question I'm really trying to answer is simple: if I add this person to the team, are they going to be a net positive for the business?
I'm scoping this to late mid-level (SWE III or so) through senior. Entry level is different, and staff is a completely different kind of interview, so that's a post for another day.
At the end of the day, when you hire somebody, they're supposed to make you more money than they cost. There should be a real ROI on their salary, benefits, and everything else. Even at a startup where you're not profitable yet, you're trying to grow the valuation, and every hire should push that forward.
That's a different question than "can they fill this seat" or "can they finish these tickets." If that's how you look at hiring, I think you're looking at it too simply, and your team is going to stall out at a certain point.
The behavioral part of the interview is where I learn the most about this. I'm looking at how someone handles ambiguity, whether they take real ownership, how they work with other people, and whether they make the people around them better.
But honestly, that list is pretty generic. Every hiring manager says they want ownership and people who handle ambiguity well. It shows up in every job description. So here's what each of those actually means to me in reality, and how I try to see it in an interview.
Handling ambiguity
In reality, ambiguity is a ticket that says "customers are saying the schedule page is slow" and nothing else. No spec, no numbers, no clear owner.
A weak engineer either waits for someone to write a spec or builds the first thing that comes to mind. A strong one asks a few sharp questions, figures out who's affected and how much it matters, makes a reasonable assumption, writes it down, and gets moving.
In an interview, I'll give a problem that's intentionally vague and watch what they do. Do they ask questions first, or charge straight into a solution?
Ownership
In reality, ownership means it's still yours after it ships. You are one of or the go-to person for that thing. You check the dashboards after the deploy. You notice the bug before support does. You follow up when another team's piece slips instead of waiting for someone to notice.
It's not "I finished my ticket."
In an interview, I'll ask about something they shipped that broke. I'm listening for whether they say "I" or "they," and what they did after it broke, not just how it got fixed.
Can I have a real conversation with them?
Including a disagreement. If I push back on something, do they get defensive, cave immediately, or actually engage with the point?
Do they think about the business?
The technical side is obviously a big part of the job, but when they make a recommendation, is the business in it? Engineering is a craft, and I care a lot about craft. If you're a carpenter, you don't build something the cheap way without a reason. But understanding why certain trade-offs have to be made in support of the business is just as important as knowing how to build it well.
This is also why I don't think managers should shield engineers from the business. A lot of people see that as the job: protect the team from the executives and the hard decisions. I think the opposite. If people understand where things actually stand, they make better decisions. If the company is cutting costs, maybe we need to look at how expensive our infrastructure is, or how we're handling AI spend. Those are calls I want senior people helping make, especially at a startup that's trying to grow.
Do they elevate everyone around them?
The best senior hires come in and the rest of the team almost feels like they need to catch up. They raise the bar just by being there.
Do they have people skills?
I think this gets discounted a lot. There's a stereotype that engineers are awkward and hard to work with, and that you shouldn't expect much from them socially. I don't buy it, and I specifically look for people who break it. Solid communication, solid soft skills, open. Not a salesperson, but someone people actually want to work with.
It narrows the pool a lot. There just aren't that many people who are strong technically and like this. But especially at the higher levels, I think it's worth it.