This small plugin shows the ‘Under construction” message on your site.
You are able to see the site if you are logged in.
Also you can see the site via special url. In that case plugin writes cookie to your browser, so you can see the site anytime. This is very useful for development. You send special link to your customer, and he can see your work. Everybody else sees “under construction” placeholder.
The plugin uses “wp_loaded” hook, so all theme styles are ignored. Plugin is very small and all functions are in one file. No need to separate css, html and php here. I had some thuughts to add some more functionality, such as specifying secret url in admin panel, and specifying logo under placeholder, but that implementation seems to be a bit better. When you finish development, you just wipe the single file and there is no need to delete unuser settings in db and unused files in media library (uploads).
Free to use, modify and distribute. Installable WordPress file here: