Asking the Right Questions About Tech
Toxic work cultures come from more than just human interactions. Technical choices can make a company very difficult to work at. And since asking about tools and technical process is a normal part of the interview process, spotting potential technical problems can be easier than some of the other problems you may face.
Judging the tools a particular company uses can be hard when you don't know the full history behind their decisions. That said, if you're going to need to deal with a particular language or other tool on a daily basis that you already know you dislike, you may choose to interpret a company's tool set as a warning sign. Finding that a company chooses to create its own solution to common problems, however, can be a more important sign. It's one of those issues that make setting your own priorities particularly important, though: Everyone is particular about the tools we work with, and learning new tools can be a much easier process than changing some aspect of a company's culture.
Documentation can offer a major warning sign before you even start work. It's not heard of for some companies to have minimal documentation (along with minimal on-boarding processes in general). If you're looking at a tech company that has released any of its code under an open source license, make a point of reviewing those repositories. That open source code probably represents the best case scenario, in terms of documentation, as well as tests and code review. Not only did the company in question decide that it was worth releasing, that open source code has probably been seen by more people than anything kept private. So, if anything concerns you about that code, you can assume that the company's private repositories have bigger problems.
Don't be afraid to ask lots of questions about the technology at a tech company. While not all companies will give you in-depth answers, especially without asking for you to sign a non-disclosure agreement (NDA), they are usually willing to discuss their stack and overall policies, if only to make sure that job applicants will be able to do the necessary work.