Tool to fill fields

I have an idea and I'm not sure how to how around it: I want to fill fields on a website using information from an excel.

My plan is to find all fields on a website, recognize the fields that need to be filled and fill them with the corresponding field data from the excel.

What tool do i need to make to recognize all the fields on a website?

And do i make a seperate tool for recognition and an app that uses the data and populates the fields?