Client Side vs Server Side Validation
In all cases, the validation takes place on the server, because the user might tamper with the HTTP communication and post a viewmodel which violates some of the validation rules.
DotVVM can do client validation for the following attributes on the client side:
DotvvmEnforceClientFormat- see the Formatting Dates and Numbers for more information.
You can turn the client validation off in the Configuration. In that case, everything will be validated only on the server.
config.ClientSideValidation = false;
If you write your own validation attributes, they will be evaluated on the server side. Currently, DotVVM doesn't support extending client validation in custom validation attributes.