Find an example of a web form that accepts entries from the user

Find an example of a web form that accepts entries from the user, such as a web-based calculator. If you were

programming this form, what validation checks should be put on each of the input fields? If possible, test the form by entering some inputs that should be invalid (be careful not to inadvertently place an order for something!). How does the application respond? Are all inputs properly validated and are the error messages clear? Would you recommend any changes to this application’s data validation?