Ads card number to trello and gives an example of how you can also count the number of cards with a specific label. The current example is useful if you mange sprints to see how many of the tasks were critical and how many extra tasks were added into the sprint.

trello-count-cards.userscript.js

// ==UserScript==
// @name         Trello Count
// @namespace    https://tcrhd.net/
// @version      0.2
// @description  Ads card number to trello and gives an example of how you can also count the number of cards with a specific label. The current example is useful if you mange sprints to see how many of the tasks were critical and how many extra tasks were added into the sprint.
// @author       Cosmin-Romeo TANASE
// @include      https://trello.com/*
// ==/UserScript==

(function() {
    'use strict';
    if ($("#boards-drawer").length<=0) return;

    function displayCardCount(){
        $("div.board-main-content div.list").each(function (){
            var cardsNo = $('a.list-card', this).length;
            var criticalNo = $('span.card-label-red', this).length;
            var extraNo = $('span.card-label-orange', this).length;

            var label = cardsNo+' cards | '+criticalNo+' critical | '+extraNo+' extra';
            $('.js-num-cards', this).text(label).removeClass('hide');
        });
    }

    setTimeout(displayCardCount, 2000); //Theoretically boards should be loaded now TODO: See how it can be injected when draw
    setInterval(displayCardCount, 30000); //To display future updates TODO: See how it can be injected when redraw
})();