Updated for Bootstrap 3.3.5 and KO 3.3.0

bootstrap.knockout.validation.js

ko.validation.init({
    insertMessages: true,
    decorateInputElement: true,
    errorElementClass: 'has-error',
    errorMessageClass: 'help-block'
});

this.first = ko.observable("Greg").extend({ required: true });

sample.html

<div class="form-group" data-bind="validationElement: first">
  <label for="inputFirst">First Name</label>
  <input class="form-control" id="inputFirst" type="text" data-bind="value: first" maxlength="100" />
</div>