I went looking for articles on how to interview programmers/engineers for startups. I didn't like much of what I found (I did like Elad Blog's take), and none of them addressed engineering skills and new-technology choices the way I wanted, so wrote my own guide (and as usual, wrote too much). My thanks to Mark Ferlatte and Rachel Gollub for reviewing a first draft of this. Mistakes remain mine.
My thesis is that a startup needs coders who are good engineers too. A startup that hires coders who are bad team players and engineers will quickly dig itself into a hole of technical debt. A startup is in a worse position than most other employers to teach engineering skills like technical teamwork, using specifications and unit testing; also it is in no position to spend 5 times as much time and money fixing bad code.
1. How do you use specifications in your programming? Please expand...
Look for mid-range answers here. “Never” or "Specs are a waste of time" is bad — using specifications, wireframes or user stories is an important skill. An engineer who doesn’t know how to review and use a specification will at best put their own assumptions and that specification's errors into code, which will turn up as bugs later.
“I always need specs” may also be bad for a startup, unless the engineer takes some responsibility e.g. “If a spec doesn’t exist, I write down what I’m going to do and send it to the team."
A good engineer should also be able to talk about reviewing specs and improving them, and possibly even writing them or teaching product people how to write them. Look for information behind the quick answer, because companies and experiences vary hugely. A developer who can talk intelligently about how rapid iteration reduces need for elaborate specs sounds decent to me.
2. How much do you rely on unit testing? When and how do you write unit tests?
Here the right point on the scale is at least 80% of the way towards “always”. Unit testing is an important skill and art and another one you don't have time to teach.
Excuses are not that impressive here. If a candidate said their past companies didn’t do unit testing I would wonder why the candidate didn’t learn and even promote unit testing on their own.
Good answers: “I rely on unit testing to help me think through a problem and I write unit tests sometimes before I write the function, but sometimes after, depending."
3. When do you decide to use a new technology? Give an example of learning a new technology, promoting it in your team, and executing it.
Look for mid-range answers here too. Candidates should not be on the bitter bleeding edge of technology. There needs to be a drastic advantage to taking on the risk of brand-new technology. Ask how they justified picking up something untested, and how they assessed and minimized the risk. See my addendum below for examples of bleeding edge vs behind the curve.
On the other hand, candidates should be able to point to some new-ish technology (not just new to the candidate), year after year, that they learned and adopted. Try to find out if a candidate eagerly learned the technology or had to. Did the candidate choose and promote, or follow teammates’ beaten paths?
4. What’s important to you in your work/employment?
Most answers are probably not critical hire/no hire factors here. However, you need to know what the candidate needs, in case 1 week later you’re saying “How do we convince Lisa to join us now” or in 6 months asking “Lisa is really awesome, how do we make sure we keep her?”. You must treat tech candidates' needs respectfully. You need them more than they need you.
That said, there are some bad answers for startups: “Working with rock stars” (or ninjas). “Stability”. “A mentor” (or a hands-on education in engineering).
Good answers: “Learning” (if self-directed). “taking on a variety of roles”. “Being very responsible for something”. “Moving fast” (if under control via unit tests, etc). “Being involved at the level of the business model.” “Having some non-trivial ownership in a venture. “ “Gain the experience to do my own startup.” “Be in a position to develop a great engineering culture." "Working with a good team."
5. Can we see some samples of your code? (Alternatives: solve problem code on the whiteboard or join for a trial day coding on the project)
For this part, you need two or more really good startup engineers that are so good you CAN’T hire them to advise you. Have them do in-person or phone interviews or read source code to evaluate candidates.
If the candidate can’t point to some open source contributions, it may be possible to see some previous code under NDA; or the developer may have done some tutorial coding to learn some new system. Looking at source code is an effective use of time both for the candidate and for your startup. If this is not possible for the candidate, then a whiteboard or “homework” coding session is needed.
Another option is to have them work on a project for a day or two. Sometimes this can work and sometimes it can't. A programmer who can't or won't dedicate full days of programming to prove themselves to a startup (see above about you need her more than she needs you) may still be the right person to hire.
What else to take notes on
While asking these questions, find out if the candidate is nice and easy to get along with. Startups are stressful enough already. Working with arrogant people makes startups worse. You need good communicators. Techies who assert and tell what to do may sound knowledgeable initially so dig deeper -- they need to be able to explain in detail how and why, too.
Try to find out if the candidate learns fast, both by asking about learning new technology, and ideally by asking making suggestions in the technical part of the interview (or after reviewing their code) that require the candidate to listen to another way of doing something and figure out how and why to do it that way.
Try to find out if the candidate can handle uncertainty and change-- the spec question is a good time to address that as a side concern.
Addendum: Examples of bleeding edge, cutting edge and behind the curve
Bleeding edge: Almost no startup in 2009-2010 needed to or could afford to build their entire codebase on Node.js that year. Don't hire the person who advocates this or something equivalent, especially if they haven't done it themselves. (Not their team.)
Cutting edge: If the candidate learned Node.js in 2010, however, and decided that 2012 was the year to make it the basis of a product, and had a plan for hiring other engineers that know or want to know Node.js, that is a good sign.
Behind the curve: They should not still be promoting Java servlets for brand-new code-bases (at least not without Hibernate and Spring, and only if Java is already needed for the startup). Somebody whose only new technology learned in the last 5 years was Java servlets, because their manager assigned it to them, is not adopting new software technology at an appropriate pace or time.
You notice that my examples are older or heavily hedged. This is a really tricky area. I disagree with people I deeply respect about whether certain examples are a bad sign, a good sign, or "it depends" -- though I suspect if we talked about a specific candidate and what that candidate had said about this question we'd be able to come to a conclusion about the candidate, even if not about Java Servlets. Take really great notes so you can talk about the nuances with at least 2 of your tech advisors.