I absolutely love this idea from Thoughtbot. Just like automated tools that check your HTML for syntax, formatting, validity, or whatever else, FormLinter checks your <form> HTML for best practices. Things like every input having a label, using correct input types, required fields, and more.
Doing all these things right is worth the effort: improvements like these improve accessibility and increase conversions. However, checking this sort of thing by hand is tedious and error-prone.
We were testing some forms in the ol' CSS-Tricks team chat and it was doing what it said on the box. On Geoff's personal site, it gave his contact form a "B" for not having matching labels for inputs and not having any fields required (seems like a fairly high grade?). The form was output from the mega-popular "Contact Form 7" for WordPress, also a bit surprising.
Many of the forms we tested bombed the app though. No word on that. Might be an HTTPS thing?