I've interviewed hundreds of folk for coding roles and indeed, I still have to do it in my own startup.

Although I myself am a coder, I still use a lot of non-coding techniques to sift through other coders. There are a few options nowadays, all of them you have to go fish a bit and there are a few pitfalls with this which can result in false positives/negatives, so don't rely on any one option as your only source of truth. Combine the results and make sure to get a decent sized historical record where they exist.

1. Go to sites like Stack Overflow and see if they are on it and what their ratings are.

2. Check if they have a GitHub account. You won't be able to verify their code, but look at how often they've done stuff recently, what they're contributing to, check their icket contributions and discussion, how many commits they've made in the codebase etc.

3. Read their blogs. Again, useful as a historical record.

4. When speaking to coders, make sure they're talking about the value they deliver to you, not just the code. Code isn't written for code's sake, it's got some value to it.

As others above have said, there is definitely mileage in evaluating the way they communicate as well. Since you'll be working with them and if they can't communicate with you, then you'll both be a bit stuck.

I've missed out a lot of detail here. Give me a prod if you need me to goo into more detail for you.