Google announced today that it will now factor in how mobile-friendly a website is when ranking your search results on a smartphone. Pages that are optimized for small screens will be boosted in the result versus those designed strictly for the desktop. This boost however, will only apply to mobile searches.

Google announced plans to take this step in February, which gives web developers time to prepare, and officially going into effect today.

“Now searchers can more easily find high quality and relevant results where text is readable without tapping or zooming, tap targets are spaced appropriately, and the page avoids unplayable content or horizontal scrolling,” the company wrote in a blog post. The change applies to searches in all languages and in all countries where Google operates.

This Change Does Not Impact Search Results on Desktops and/or Tablets

Google further noted that the “mobile-friendly update” won’t affect your top hit for every search query. If the content on a website is a better match for a given search phrase, you will still likely to see that page given priority — regardless of how it looks on a phone.

“We still use a variety of signals to rank search results,” said a company spokesperson. And since tablets and their larger displays offer a browsing experience that’s relatively closer to PCs, the mobile-friendly policy does not extend to those device; it only shifts around rankings on smartphones.

Still, the change is sure to dramatically affect search-generated mobile traffic. For websites that are prepared and optimized for mobile, it’ll be a positive shift. Those that aren’t may see a dip in traffic until they update to better accommodate mobile users. If you’re unsure where a site lands on mobile friendliness, here’s tool to determine a site’s mobile friendliness that can scan its design fast and give a thumbs up or thumbs down based on Google’s criteria.