Block Site
Block Site (formerly known as Stop Social Media) is a simple Chrome extension that improves your productivity by blocking the access to time-consuming websites (like during the working hours) as you specify in Options. Block Site is by default disabled and doesn't block any website until you say so in Options.
Options
To open Options, right-click on the Block Site icon in the toolbar (looks like a letter B) and choose Options from the menu.
Example
The sites you decide to block to boost your productivity, is up to you. Here's an example:
facebook.com
instagram.com
youtube.com
twitter.com
reddit.com
See Options to configure.