Link building efforts for SEO completely rely on crawlable links that search engine bots can crawled. Link building has always being an important part of marketing and optimizing web sites and web marketers can often get distracted by quantity goals rather than quality.
But what exactly is a crawlable link?

It is one that is not blocked from bots with robots.txt, NoIndex meta tag, javaScript redirect or NoFollow tag.

Here are a few important things you need to have a look:

1. Have a look at the robots meta tag, look at the page source code. If there is no robots tag, then that's fine.

However,if there is a robots meta tag and it looks like this,
meta name = “robots” content = “index, follow”
that’s good

But, if the robots meta tag looks like this:

“robots” content = “noindex, nofollow”

OR
“robots” content = “index, nofollow”

that’s is not worth from SEO point of view.

2. There might be a JavaScript redirect of links from a desired page, put your cursor over the link and look at the url that appears in the status bar at the bottom of the browser. If it shows the correct link url, then in most cases, it’s ok.

3. Check if robots.txt is blocking search engine spiders from crawling links on a page, then add the text “/robots.txt” to the end of the URL in question.

For example:

http://www.exampl.com/robots.txt

you may find something like this:

User-agent: *
Disallow: /administrator/
Disallow: /cache/
Disallow: /components/
Disallow: /editor/
Disallow: /help/
Disallow: /images/
Disallow: /installation/

What the “disallow” instruction does above is to tell search engine spiders not to crawl the designated directories. In the case of the article sharing site above, if any articles are located in one of these directories, then the links within those articles to client sites are no good for SEO benefit. However, readers can still click on the links and arrive at the indicated destination.

4. There might be a no follow tag, right click on the link URL using a browser like MSIE or Firefox and click on “Properties”. See if there is an attribute called:

rel = nofollow.
If that’s there, it’s not important from SEO point of view.

If it’s not there at all or has another value besides “nofollow” then it’s probably ok.

Link building as a result of creating and promoting content worth linking to is high value, high impact and very scalable. However, if it is important to check link sources to determine their value for SEO benefit you can use the above methods, create your own script to check them automatically.