The system needs one server-side view, and some client-side JavaScript. You can find the view code in my Django snippets Git repository. The view only works with POST requests. It takes a standard HttpRequest and some options:

• form_class: this parameter defines the newforms class to validate against. It can be specified in the extra args parameter of the view’s urlconf. If you don’t specify it, the ‘form_class’ POST field will be used. If this doesn’t exist either, an exception is raised. The parameter can be a newforms form instance, a string, or a class (which should be a subclass of BaseForm).
• format: the serialization format to use. Currently only ‘json’ is supported.
• args: extra argument list to provide to the form constructor (shouldn’t be provided in most cases)
• kwargs: extra argument dics to provide to the form constructor (shouldn’t be provided in most cases)

Next to the server-side view you’ll need some pretty basic JavaScript code on client side. I use JQuery and the JQuery Form plugin. Here’s some sample code, assuming the form ID is ‘my_form’, and form fields are represented like this:

<p id="{{ form.field.name }}_container"><label for="{{ form.field.auto_id }}">{{ form.field.label|capfirst }}:</label>{{ form.field }}
{% if form.field.errors %}<span id="{{ form.field.name }}_error" class="error">{{ form.field.errors.0 }}</span>{% endif %}
</p>

Here’s the corresponding JavaScript code:

function do_something() {
}
function process_validation(data) {
    if(data['form_valid'] == true) {
        do_something();
        return;
    }
    for(var field in data["errors"]) {
        errors = data["errors"][field]
        if(errors.length > 0) {
            error = errors[0];
            if($("#" + field + "_error").length == 0) {
                s = $("<br /><span style=\"display: none;\" id=\"" + field + "_error\" class=\"error\">" + error + "</span>");
                $("#" + field + "_container").append(s);
            }
            $("#" + field + "_error").html(error).fadeIn("slow");
        }
    }
}
function validate_form(data) {
    data.push({name: 'form_class', value: 'project.application.forms.ApplicationForm'});
    $.post("{% url validate_form %}", data, process_validation, "json");
}
$(document).ready(function() {
    $("#my_form").submit(function() {
        data = $("#my_form").formToArray();
        $(".error").fadeOut("slow");
        validate_form(data);
        return false;
    });
});

Obviously this should be changed to suit your needs.

I hope this code can be useful for someone…