How much is a keyword worth to your website? If you own an online shoe store, do you make more sales from visitors searching for "brown shoes" or "black boots"? The keywords visitors type into search engines are often available to webmasters, and keyword research tools allow us to find this information. However, those tools cannot show us directly how valuable it is to receive traffic from those searches. To understand the value of a keyword, we need to understand our own websites, make some hypotheses, test, and repeat—the classic web marketing formula.
Hey Alex – this is a good question. No tool is going to be spot on. My advice is to not look too much into the accuracy of the metrics, but look at it more as a relative measure. I’m finding Ahrefs to be a good barometer for keyword competitiveness, but I’ve also heard great things about KW Finder lately. I think it’ll more come to personal preference. Both are solid options.
Answer: Google Keyword Planner was created to find keywords for Google ads. It will likely not produce very good keyword suggestions for SEO or content marketing purposes. Google Keyword Planner often hides good long tail keywords. To find long tail keywords for SEO, you can use Keyword Planner alternatives such as Google Trends, Google Suggest or Keyword Tool.
Note: If you can’t justify using Ahrefs on a monthly basis, you could sign up for a month, do your KW research and cancel. That said, if you can justify the monthly pricing it’s well worth keeping because you’ll get access to the ongoing functionality such as rank tracking and web monitoring. It also means there’s no need to use any other tools to track rankings or monitor mentions on the web.
They’ll show you information like how many external links the site has, the number of Facebook and Google+ shares, estimated visits per month, and its page authority. All of this is valuable intel that can give you insight into where your page could potentially rank against them, without needing to do more research with a separate tool or on another page.

This is a rather crude metric because it presumes one can monetize all the traffic they receive AND one can generate as much profit per visitor as Google does. Anyone who could do both of those would likely displace Google as the first consumer destination in their market (like how many people in the United States start ecommerce searches on Amazon.com rather than Google.com).
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input.  In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).
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