Unexpected circumstances have meant I've done two job hunts in recent months. I usually scribble down a handful of questions to ask or consider prior to each interview. Here they are so I can remember and refine them over time.
What does the business do? Who's the target market? What's the dream? How big to you want to get etc?
How long have you been around? Are you profitable? Have you taken VC? Who are the main people strategically driving the direction of the business?
How big's the dev team? How many people? What roles? Full timers, part timers, contractors? How long have the core members been there? Who would I be reporting to and working with most closely?
How's the leadership structured, and how's work delegated? Top down? Flat? Collaborative? Do you follow any specific development methodologies?
What tech stack are you using? (and subsequently… you mentioned X an Y, which I don't have experience with. Are you OK with that?) They should at least be fine with you not knowing peripheral technologies in their stack.
Are you open to remote work? Does anyone actually work remotely? If so, how often? Have you found it good / bad / indifferent? What are typical work hours? Are you flexible with the times people work? Do people take advantage of that flexibility?
Being "open to remote work" and having people who actually do it are two different things. Likewise for flexible work times.
What will I learn from a technical standpoint in this role?
What are the career growth opportunities - both within this role / company, and if I were to move on in a year or two's time?
How do you manage technical debt and maintain code quality?
There are lots of valid answers to this. A vague answer is a red flag.
Do you pay for employees to go to Ruby Conf and Rails Camp (or other equivalents)? Do you do anything else regarding ongoing professional development for your employees? A "yes" here is good and reveals a lot about general attitude towards employees.
What are your expectations regarding pay?
I used to be very uncomfortable talking about pay. One of the best life skills you can get is the ability to talk about it in a confident, upfront, open manner.
Edits: additional questions / comments given to me on twitter:
Rebecca: "some of those would be useful to ask to both the employer, and one of the devs you would be working with. Compare the answers."
Pat: I'd be asking questions about culture and diversity - is it on the company's radar? How are they addressing such things?
and: I'd also be keen to hear about leadership (top-down, collaborative, etc) and ownership (profit-sharing? equity?)
Rudy: I'd throw in something along the line of: "how do you measure my performance?" type question too ;)
Garrow: how do you decide what gets built? Who does that? How do you measure the success of built thing?
Andrew: do you have any references? (I have to provide them, so where are yours?)