How should my short URL be set up to redirect to my main URL to avoid duplicate content issues?

• My main site is a long keyword relevant URL that's 17 characters long. For that reason I've registered and activated a shorter URL with just 5 characters that 301 redirects to the main site.

  My question is; to avoid duplicate content issues, how do I stop Google from listing the shorter domain?

Answer:

Assuming your 301 redirect is functioning properly, this should prevent Google from surfacing the short domain in search.

However it will likely show up if you do a site:short.com site-search even though your current 301 redirect will likely prevent Google from showing anything other than the home page.

Therefore, this shouldn't really be a problem because the redirects should prevent Google from seeing it as a duplicate site.

Pro tip: You could make the short.com requests go 404 page missing by deleting the home page temporarily, remove the redirect, and then go to Google Search Console and remove the home page for that domain.

After it's been removed, then add the robots.txt block...

User-agent: *
Disallow: /

...to keep the site from surfacing at all. Then you can just add the redirect back in.

In the future, prior to making the short domain live, you should first put in the robots.txt block to avoid having to do the above described "fix" — after which you can then add the redirect.