Force trailing slash in htaccess

Writing .htaccess rules can be trick and may have several approaches in achieving the same goal.

So in this case, redirecting website URLs with trailing slash of as usually called FORCING trailing slash in URLs.

You can use this universal condition

RewriteCond %{REQUEST_URI} /+[^\.]+$
RewriteRule ^(.+[^/])$ %{REQUEST_URI}/ [R=301,L]

Now if you want to exclude a page or a particular extension like .php:

RewriteCond %{REQUEST_URI} !^/excludethispage\.php

or

RewriteCond %{REQUEST_URI} !^/excludethistoo

Putting them all together:

RewriteCond %{REQUEST_URI} !^/excludethispage\.php
RewriteCond %{REQUEST_URI} /+[^\.]+$
RewriteRule ^(.+[^/])$ %{REQUEST_URI}/ [R=301,L]