The editor is flexible in that it allows you to both modify existing code or add your own. Doing this allows you to extend the functionality of the platform and provides you with additional features. For example, you can add a custom calendar widget or even a third-party custom contact form for taking payments on your site. ### Warning Developer mode is not available when you are editing the site in flex mode in the Classic Editor. You must exit flex mode to access Developer Mode. ## How to Add Custom Code There are several ways you can add custom code: via developer mode or the HTML widget. Following are instructions on how to access both. ### Note * Custom code that is intended to be visible in the site should be added using a HTML widget. Custom code that is not visible should usually be put in the header. In general, it is always best to first follow the directions provided by the code's writer before adding it to your site. * You cannot upload or run PHP files. Server-side languages, such as PHP, are not supported, as the platform does not provide server-side execution or filesystem access. ### Developer Mode Developer Mode gives you access to edit and change your site's HTML and CSS. Adding custom code allows for advanced customization that is not possible with the drag and drop editor, however this should only be performed by advanced users with a solid understanding of web development code. To access Developer Mode: 1. Click **Developer Mode** (![Developer mode icon](/docs/39024760766999-68.png)) in the navigation bar. Alternatively, right-click on a widget and select **Edit HTML/CSS**, and then click **Dev Mode** in the lower left. 2. After adding your code, use the **Save** and **Preview** buttons to see your work. ### HTML Widget The HTML widget is the easiest method of adding custom code to your site. Depending on where you place your HTML widget, it will either appear on all pages of your site or just a single page. If you place the HTML widget in either the header or the footer, it will be placed on all pages of the site at the same time. This is because every site shares the header and footer. If you place the HTML widget anywhere else, it will appear only in the body. To add an HTML widget: 1. In the side panel, click **Add**, then click **Widgets**. 2. Search for **HTML**, then drag and drop the widget into a column or row on your site and then paste in your code. ## Custom Code in the Header You can place code in the site-wide header or the header for an individual page. ### Note Consent management apps are not able to prevent code from running prior to consent when the code is placed in the header HTML. This is because we optimize the structure and order of how content loads, based on performance best practices on the site. We place scripts and CMP banners lower on the page, in order to improve the performance of primary content. Because of this, it is recommended to place code in the body-end when using a consent management app. ### Site-Wide Header To place the code in the site-wide header: 1. In the side panel, click **More**, then click **Settings**. 2. Click **Header HTML**. * _Head HTML_. Add content to the head section field. * _Body End HTML_. Add custom HTML/Javascript just before the closing tag of the element for each page in the site. 3. Paste your code, then save. ### Single Page Header To place the code in the header of a single page: 1. In the side panel, click **Pages**. 2. On the page, you want to add it into, click on the **settings** icon (![Gray gear icon named settings icon](/docs/39024760519831-69.png)). 3. Click **SEO**. 4. Scroll down to **Header HTML**. 5. Paste in your code here and save. ### My Code is Disappearing When I Place it in the Head Section It is common for pixel tracking codes to disappear when placed in the header. The head section `` does not accept any code that is ``, `