Set Default Post Editor Mode in WordPress

Some prefer to work with the visual editor when writing posts and others prefer the text editor. Change the default post editor by adding the following lines to your functions.php file:

# Visual Editor as default
add_filter( 'wp_default_editor', create_function('', 'return "tinymce";') );

# HTML Editor as default
add_filter( 'wp_default_editor', create_function('', 'return "html";') );

For more editor configuration, see Enable Gutenberg for Custom Post Types.