How to set limit to RTE for limited chars

[lone_Ranger]

This Blog worked for me. 
URL-
richtext-max-characters-length-validation 

[BrianKasingli · Accepted solution]

You must create a new AEM ClientLibrary, and introducing a new Jquery Validator like this,

;(function (window, $) {
    'use strict';
    /**
    * Rich-Text Editor Max Length Validation
    *
    * @class RichTextMaxLengthValidation
    * @classdesc registers a new validator to the foundation-registry service focused on the
    * cq/gui/components/authoring/dialog/richtext component.
    *
    * Usage: the attribute maxlength to the richtext component, example: maxlength="100"
    */
    var RichTextMaxLengthValidation= function () {
        var CONST = {
            TARGET_GRANITE_UI: '.coral-RichText-editable',
            ERROR_MESSAGE: 'Your text length is {0} but character limit is {1}!',
        };
        /**
         * Initializes the RichTextMaxLengthValidation
         */
        function init() {
            // register the validator which includes the validate algorithm
            $(window).adaptTo('foundation-registry').register('foundation.validation.validator', {
                selector: CONST.TARGET_GRANITE_UI,
                validate: function (el) {
                    var $rteField = $(el);
                    var $field = $rteField.closest('.richtext-container').find('input.coral-Form-field');
                    var maxLength = $field.data('maxlength');
                    var textLength = $rteField.text().trim().length;
                    if (maxLength && textLength > maxLength) {
                        return Granite.I18n.get(CONST.ERROR_MESSAGE, [textLength, maxLength]);
                    }
                    return null;
                }
            });
            // execute Jquery Validation onKeyUp
            $(document).on('keyup', CONST.TARGET_GRANITE_UI, function (e) {
                executeJqueryValidation($(this));
            });
        }
        /**
         * Execute foundation.validation.validator's validate algorithm.
         */
        function executeJqueryValidation(el) {
            var validationApi = el.adaptTo('foundation-validation');
            if (validationApi) {
                validationApi.checkValidity();
                validationApi.updateUI();
            }
        }
        return {
            init: init
        }
    }();
    RichTextMaxLengthValidation.init();
})(window, Granite.$);

There's a full tutorial that I have written, and you can check it out here, https://sourcedcode.com/blog/aem/touch-ui/aem-richtext-max-characters-length-validation