Job history is an important issue to raise in an interview, but I wouldn't be so quick to make a decision solely on this metric, and before an actual interview because it can be deceiving.
The previous comments brought up some good points, but I found them a bit too generalized, some going as far as saying that quick succession of companies indicates a candidate you should be avoiding. I think that's a poor argument so I'll try to describe how this could be your best candidate.
I would take into account a few factors, before deciding:
- Candidate years of experience
- Candidate level of knowledge
- Candidate attitude, drive, motivation (you can tell that during an interview)
- Companies the candidate worked for
- Candidate responsibilities in those companies
- Last, but not least, ask yourself, what kind of company is your company? (the one you're hiring for)
I would also bring up the issue in the interview and ask for the candidate's opinion.
Now let me detail a bit as to why so many factors, and why this decision isn't really a black/white one and there's always a chance you get it wrong.
First of all an important metric is the number of years of experience and the level of knowledge. This will usually tell you how passionate the candidate is, and give you an idea of the professional growth.
The companies the candidate has worked for is also important to understand and correlate that with the candidate's drive/motivation/ambition.
Like previous posters said there all sorts of companies from startups to enterprises, and the differences in working environments are all over the map.
Similarly there are all sorts of candidates from really incompetent to very capable and mentalities from this-is-just-a-9-to-5-job-I-can't-wait-to-get-home-and-forget-about-all-this-crap.-What-time-is-it? to passionate people who see it as a craft and want to get better at it.
The tricky thing is that a successful match for your company might not involve picking the candidate with the best attributes from that list. It has to do a lot with your company's culture also. It's a well observed fact that in companies with poor management for instance, or really boring and repetitive work, or a bad working environment, the best people tend to leave first, the competent might leave at a certain point in time, and the poorly qualified tend to stick forever. The reason is fairly simple. Qualified people won't put up with a bad environment because it pretty much conflicts with the craft bit I was mentioning. They care too much about the work to do it in a poor way, or see that their input is not being valued, or a general indifference to the output of their work. They are confident enough in their skills to leave a s(t)inking ship. And this might involve leaving during the first year. They usually don't have problems finding a new job because, well, they're good at what they do.
Recruiters and interviewers usually ask why they took the job in the first place? Well, just as it's difficult to tell from an interview how good exactly or motivated a candidate is, the same is true for the candidate trying to figure out what the working environment at that particular company is, before actually starting to work there.
If you're a small company looking for a candidate who is passionate about his work, ambition and drive are the most important qualities, and those little nr of years with a number of companies doesn't mean anything. He's probably the candidate you want. Being involved in the product and wearing different hats to get the work done.
If on the other hand your company has a position available for back-end developer with predefined specs for the next 5 years then I would go a bit further and try to find out what he sees as an ideal position. Is this candidate interested in exploring a domain to its deepest, or is he/she driven more towards innovation and passionate about new technologies and opportunities to put them to practice. You really need to match a candidate to the job you're offering. Otherwise, even if they're qualified, they'll leave.
Also, the startup mentality of let's-figure-out-how-to-do doesn't really fit in with enterprise jobs, and the enterprise mentality of give-me-the-specs-that-tell-me-how-to-do doesn't really fit in with startup/small company jobs.
If you're hiring for the enterprise I guess small number of years might tell you a bit more than if you're hiring for a small company.
But generally, number of years alone doesn't really mean anything. It could either describe an incompetent candidate or a competent candidate who's just looking for a better working environment with better opportunities to grow professionally.
Personally I have a new thing where every half year I look back over the previous half and try to estimate how much I had the opportunity to learn/ what can I do to improve. If I'm really at a stuck point where I'm not really accumulating any knowledge and I can't manage to influence the situation for the better, I will just leave. There's no point in wasting any more time. It's too precious. And I'm not counting myself as one the elites here. I'm just saying, why waste time when you could put it to better use, and be more satisfied professionally and with your work.
Same goes for competent people. It's not that they're purposely leaving companies after 1 year, it's just that they haven't found the right one to spend the next five years with.