It gives you instant access to the following Page and Domain metrics:
Domain Rating (DR);
URL Rating (UR);
Estimated Organic Search Traffic (ST);
Number of ranking keywords (KW);
Number of referring domains (RD);
Number of backlinks (BL).
Besides, you can see all of these metrics right below every page ranking for the keyword you're searching for.
In addition to this, Ahrefs SEO Toolbar will show you the most important keyword metrics right on the SERP:
Search volume (both Global and Country-specific);
Keyword Difficulty (KD);
Cost per Click (CPC).
Installing the Toolbar
Installing the toolbar is easy.
For Chrome users, head to this link and install it.
For Firefox users, head to this link and install it.
Usage and consumption
Ahrefs SEO Toolbar provides a bunch of free features. However, you need an active paid account at ahrefs.com to get SEO metrics.
To show you the SEO metrics, the Toolbar consumes the "Export rows per month" credits in your account: 1 row per URL.
This means that it costs one export row credit to show page and domain metrics for the URL that you visit when the metrics bar is on or when you request the metrics by clicking on the extension icon.
Getting SEO metrics for the search results on SERP also costs one credit per result. So with the traditional 10-results SERP page, ten credits will be spent.
Keyword metrics shown under the search bar also consume one “Export rows per month”.
No export rows will be spent if the metrics display is disabled in the Toolbar settings.
What features are free?
Even if you don't have a paid subscription, Ahrefs SEO Toolbar provides a lot of tools and reports for free:
On-page SEO report, including details about page titles, descriptions, canonicals, hreflangs, sub-headers, crawl-ability/index-ability, social tags, etc., is free. (the Content and Indexability tabs)
Outgoing link checker
Redirect tracer and HTTP headers reader
Location changer for SERP