Are user-controlled friendly URLs automatically handled by Google?

Question

I have a Friendly URL system exactly like Stack Overflow.

So /car/123/blue-subaru-1993 is a link.

But as users have the ability to change the title of the listing, it could soon become:

/car/123/awesome-blue-subaru-1993

I'm worried (but unsure) that if Google re-indexed my site, It would now have two links pointing to the same content? Or does Google completely re-index and would realise that the previous link does no longer exist?

To clarify:

1. The site doesn't use 301 Moved Permanently

2. /car/123/title is mapped using a routing config file to an action

Answer 1

Assuming your server is set up properly Google will have no issues handling this. If the old URL no longer works then your server should be sending a 404 HTTP Response Code, or better yet, a 410 gone, which will tell Google that the page cannot be found and, after receiving this error multiple times, they will remove this page from their index.

However, this is not ideal from an SEO standpoint. Any links to your old URL are now broken and offer your site no value. You're shooting yourself in the foot by throwing them away. What you should be doing is whenever a user changes the URL of a page is sending a 301 redirect to the new URL whenever the old URL is requested. This will not only help users find the page they were looking for (whether through stake search results or links from other sites) but it will tell Google that any links pointing to the old URL should be credited to the new URL. This will allow the page to retain all of the positive SEO factors that incoming links provide. Links are votes. Not all links are equal but that doesn't mean you want to throw them all away.

FYI, if for some reason both the old and new URL pull up the same page (because you are not doing a redirect of any kind) then you will ultimately run into duplicate content issues. Google is actively seeking to weed out duplicate content, which it views as low quality, and if your site contains enough of it your entire site may be penalized. If this is the case, and based on your comments this is happening, you can either go and implement the 301 redirects, or use canonical URLs. These tell Google which page to consider the "main" page and they will show that one in their search results. Check the course of this page. Stack Overflow uses canonical URLs because their pages can be pulled up by thousands of different URLs. This guarantees that Google knows which one is the main one and prevents duplicate content issues for them. (FYI, Google doesn't see the routing you do behind the scenes. They only see the URL they requested and the content it serves).

Also worth considering, if your URLs keep changing, search engines may have difficulty finding your new pages, especially if you do not provide a redirect or canonical URL. If you're not doing so already, I recommend using an XML sitemap. They're easy to implement and keep all of the major search engines aware of the location of your content.