Permalink redirects for SEO in WordPress

I never noticed this, but if you type into your browser window

http://mydomain.com/postname/

and

http://mydomain.com/postname

they open up like two different pages.  The only difference is the trailing slash, but because WordPress doesn’t distinguish between them, it’ll open them either way.  This means, to a search engine bot, you have two identical pages.  The phrase “duplicate content” comes to mind.

Simple solution: Permalink Redirect is a plugin that you install (one file) and activate, and boom, the slash will be added whether or not people type it in (or find it that way in a link from elsewhere).