Adding a character limit to a Contact Form 7 text box requires a little bit of code to make it work.
The trick: You can’t use a textarea, it must be just a text field.
The code: text your-name 100/140 will give you a single line text box that is 100 characters wide and has a character limit of 140 characters.
To make the box mandatory, add a * after the text: text* your-name 100/140
It’s as beautifully simple as that.