Options -MultiViews
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^\.]+)$ $1.html [NC,L]

#PRODUCTION remove extension and add trailing backslash
#RewriteEngine On
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteRule ^([^/]+)/$ $1.html
#RewriteRule ^([^/]+)/([^/]+)/$ /$1/$2.html
#RewriteCond %{REQUEST_FILENAME} !-f
#RewriteCond %{REQUEST_FILENAME} !-d
#RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5}|/)$
#RewriteRule (.*)$ /$1/ [R=301,L]