No doubt, if you use a tool like GTMetrix, you’ve seen a warning telling you to serve your resources from consistent URLs. The warning will tell you that the resources listed have got identical content in them but are not being served from the same URLs.
Serving from consistent URLs not only saves resources and time on fewer requests, it can also save in bandwidth.
Why Does This Happen?
All websites use resources like JS files, CSS files, images and so on to deliver the right layout, the right functionality and a better user experience. Every resource is individually called by a browser when the webpage is accessed, and these are called HTTP requests.
Most of the time, each of the resources are served from one URL but, on occasion, a resource may be available through several domains or hostnames. That means that, when that page is loaded, it gets called several times and downloaded several times, once from each URL. This causes slower page loading.
This tends to happen when a resource is shared between multiple sub-directories or sub-domains on the same website or, sometimes when multiple plugins use the same eternal resources or libraries.
In short, it is down to redirects that have not been properly implemented, the wrong settings in your CDN or even a bug inside the theme you use. This all results in multiple HTTP requests, multiple downloads and even multiple DNS lookups, all of which have a negative effect on SEO and on page speed.
How Do You Serve Resources from Consistent URLs?
The four main situations that result in duplicate resources are:
- When there is an HTTP and an HTTPS version of a website
- When two websites share the same resources
- When two or more plugins are sharing resources
- When a CDN hosts resources and those resources can be accessed through the origin server and the CDN
And the methods to solve this issue are:
Move
The commonest issue is resources shared between several linked sites or subdomains. The solution is for the filename to be served from one hostname and linked to from the other. Although an extra DNS lookup is needed, the benefits reaped from caching make it worthwhile.
Rewrite
When you use a CDN for speeding up your website, you may get duplicate resources usually caused by the way that your plugins or theme handle the static resources. Normally you would edit the URLs for the static resources manually or through a plugin, thus moving them to the CDN.
Most of the time, this goes smoothly but sometimes a plugin or theme will pull some of the files out of the media library, into the code. The solution is to go into your theme’s files and change the path so that it points to the CDN file.
Doing it manually is not the best way; instead, go into the header.php file and find the line that defines the path the content, usually a logo, and edit it so it matches the CDN resource.
Redirect
If your website is available at two different addresses, such as mysite.com and www.mysitecom, you may end up with duplicate resources. Although you might have a good reason for having your website constructed in this way, you do end up with two websites.
One is hosted on the domain root and the other on the subdomain. The solution is to choose the main website and use 301 redirects sitewide. This will tell browsers and search engines to forget the other versions and go straight to the main site.
Canonical Tag
You can also use canonical tags to consolidate resources, useful for e-commerce sites where multiple pages may point to a single resource using different attributes or categories. In all honesty, a canonical tag shouldn’t be your first choice if you can use redirects instead. Rather than removing duplicate resources, canonicals just tell a search engine to prefer a specific version of your content
To implement a canonical tag, add the link to the resource you want into the code of the duplicate resource using the canonical attribute of rel=.
Plugins
Sometimes the issues will be caused by several plugins trying to share a resource or one plugin adding a string, like ?dshd=343, for example, to the original URL. The best way to solve this is to deactivate one or more plugins.
You can’t control a plugin because it is a third-party product so all you can do is deactivate. To see which one/s need to be deactivated, turn the settings off for each one and then on again to see which cause the problem.
Whichever solution works for you will result in your website speed increasing and fewer resources being used.