Попробуйте что-то подобное в вашем коде
from wtforms.widgets.html5 import URLInput, Input
OR
from flask_wtf import FlaskForm as Form
from wtforms import (StringField, SubmitField)
from wtforms.validators import (DataRequired, Regexp)
# And then create your form with something like the following code
class WhateverForm(Form):
name = StringField('Name*', validators=[
DataRequired('Name is required'),])
url = StringField('URL*', validators=[
DataRequired('URL is required'),
Regexp('^(http|https):\/\/[\w.\-]+(\.[\w.\-]+)+.*$', 0,
'URL must be a valid link')])
submit = SubmitField()