Google Tag Manager
Google Tag Manager is a free tool that consolidates your website tags with a single snippet of code and makes it easy to manage tags--including analytics, conversion tracking, remarketing, & more--from a web interface. You can add and update tags with just a few clicks, without rewriting site code.
Google Tag Manager gives marketers greater flexibility, and it gives webmasters the freedom to focus on other important tasks. It's built to handle your tagging needs, and it works with both Google and non-Google tags. We’ve packed in lots of great features, including:
-- Asynchronous tag loading—so your tags can fire faster without getting in each other's way, and without slowing down the user-visible part of the page
-- Easy-to-use tag templates, so marketers can quickly add tags with our web interface, as well as support for custom tags.
-- Error-prevention tools like Preview mode (so you can see proposed changes before implementing them), the Debug Console, and Version History to ensure that new tags won’t break your site.
-- User permissions and multi-account functionality to make it easy for large teams and agencies and clients to work together with appropriate levels of access.