There are lots of accessibility auditing tools that exist right now. Lots of them scan websites to detect existing accessibility issues. While that's great, it's a little late in the game to get into accessibility. Web accessibility should be a part of any website every step of the way.
Using Atom, I built a plugin to let developers easily scan their code for common HTML accessibility errors. These are errors that I've commonly found on websites - not ones that are explicitly mentioned in web accessibility guidelines. Guidelines are certainly important, but can be hard to apply to actual code. By covering specific errors that people make, the plugin is more effective than going over code with WCAG 2.0 AA guidelines up on your phone.
This plugin has a long way to go. I'd like to make it more visibly appealing. I'd also like to offer an auto-fix option that fills in the error with the correct text.