Few things make online content publishers more worried than when Google changes its search engine algorithm. Many sites rely on Google for a huge portion of their traffic, and thus will be keeping a close eye on any algorithm changes—which often take effect without advanced notice from Google (GOOGL).

But this week, Google did just that—making it known that, on Tuesday, it would change its algorithm algorithm. The move—aimed at favoring “mobile friendly” sites in search results—has been expected to have a “significant impact” on search results, Google said in a blog post. The result is that mobile-friendly websites will begin to rank higher on Google search results, meaning websites without mobile-optimized sites will suffer.

The shift has been called “Mobilegeddon” by many.

Promoting mobile-friendly websites is a logical move for Google, as more and more people are surfing the Web via their smartphones. But what, exactly, does Google consider a mobile-friendly site? Here is what you need to know, along with some tips on how to deal with Google’s “mobile friendly” algorithm change—or mobilegeddon, if you will.

First things first: to see if a site meets Google’s mobile friendly standards, Google has created a test to analyze a URL and report if the page has a mobile-friendly design. (Chicago Inno is in the clear, but parts of websites like the BBC and Wikipedia currently fail the test, which will likely result in a loss of web traffic).

Mobile-friendly criteria includes things like how well content fits in the mobile screen, text size, and the space between links, according to the BBC.

Here are some other mobile-friendly tips websites should be aware of, according to Bob Buffone, founder and CTO of Yottaa, a software company for improving website loading times:

  1. Eliminate misaligned technology: Make sure mobile users aren’t presented with Flash content or other software that doesn’t run ubiquitously (or at all) across mobile devices
  2. Don’t force users to pinch & zoom: Size page dimensions and fonts to correlate with the user’s form factor and viewport without scrolling or zooming
  3. Right-size content and images: Just because mobile browsers can resize images, you’re still forcing the user to download more content and drain the device’s battery and delaying engagement
  4. Tailor to touch: Ensure buttons, links and other CTAs are placed/spaced to allow users to tap correctly

Google also has a guide for making your website mobile friendly.

So be sure to check if your site will be impacted by the algorithm change, and if so, you better act fast. You’ve got less than a day before the changes take effect.

Creative Commons Image via Flickr.