Open Site Explorer is the tool you need to rank better in the search engines and compare your site against your competitors.Some of the functionality provided by open site explorer.

Domain and Page Authority scores are  calculated : Domain Authority is the best prediction about how content would perform in search engine rankings on one site vs. another. Page Authority answers the same question for an individual page. 

URL level mozRank and mozTrust  are calculated :mozRank is global link popularity score.It is similar in premise to Google's original PageRank metric but is updated more frequently and offers greater precision. It is on a log scale and computed to be between 1 and 10. The average mozRank on what most people think of as the normal web is about 3.00.mozTrust is  global link trust score,It is similar to mozRank but rather than taking measuring link value, it measure link trust.

Domain level mozRank and mozTrust  are calculated :Domain mozRank is exactly like mozRank but it is calculated on the Domain level rather than the URL level.

Internal vs External Links : An internal link is a link from one root domain to the same root domain.An external link is a link from one root domain to an entirely different root domain.

Followed vs Nofollowed Links :Followed links are not marked and pass link juice (Ranking Power)
Nofollowed links are marked (with either rel="nofollow" or meta robots nofollow) and do not pass link juice (Ranking Power)

Anchor Text & AltText :Anchor Text & Alt Text are meta data that are important to both humans and search engines.Anchor text is the text that is visible when reading a link. This text is established in the HTML code for a link.Alt Text is the text that is displayed when an image can't be.Alt Text is established in the HTML code for an image.

301s, 302s, and Meta Refreshes :301s, 302s and meta refreshes are all ways of redirecting one URL to a different URL.
301 refers to the HTTP Status Code for this type of redirect. A 301 Redirect is a permanent redirect and passed between 90-99% of link juice (Ranking Power)
302 also refers to the HTTP Status Code for this type of redirect. A 302 Redirect is a temporary redirect and passes 0% of link juice (Ranking Power). This is bad for SEO.
Meta refreshes are a different type of redirect that is executed on the page level rather than the server level

Img Links:Image links are links that appear as images instead of text in HTML documents. These are common navigational elements on websites as buttons and global navigation.
They pass juice just like other links but don't necessarily include anchor text 

Number of Links vs Number of Linking Root Domains:Number of links and number of linking root domains are similar but different metrics.
Number of links (# of links) includes the total amount of links from all websites. Two links from the same website would be included twice.
Number of linking root domains (# of linking root domains) includes only the number of unique root domains linking. Two links from the same website would only be counted as one linking root domain. 

Guest Free PRO
Reports Per Day 3 Unlimited Unlimited
Number of Links AvailableUp to 200 Up to 1,000Up to 10,000
Number of Metrics Displayed Top 5 Top 20 ALL
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