WordPress

The OpenCookies plugin.

Nothing to enter: on activation, the plugin creates your site’s banner and loads it first in the header of every page.

Installation

Download the plugin (.zip) then, in WordPress: Plugins > Add New > Upload Plugin, and activate it. That’s all: the banner is created and active.
Optional: Settings > OpenCookies > “Customize my banner” to choose your e-mail and edit the texts and colors.
In your OpenCookies account, Tests tab: run a test to check that nothing loads before the choice.

What the plugin does

Adds the banner line at the very top of <head>, before the other plugins.
Automatically marks, before each page is sent, the tracking tags written by the theme or extensions (measurement, advertising, social networks, video): nothing loads before the visitor’s consent, with nothing to configure.
Stores nothing but the site key. The text, colors and measurement mode are set in your account.

Scripts added by hand in a theme or a “custom code” extension are also blocked by the banner, but only if it loads before them: this is the case with this plugin.