Unfortunately, most articles pointing this out come from right-wing outlets, because they're the ones incentivized to put in the work. I don't think that negates the facts (pun-ish unintended), because you can investigate the claims yourself. Here, though, is a Forbes article detailing how they engage is coverups of their own political punditry: https://www.forbes.com/sites/theapothecary/2013/12/27/in-200...

Isn't that convenient? The only sources that document this widespread, omnipresent bias against right-wing are far-right "news" organizations who themselves engage in endless propaganda.

BTW, that forbes article doesn't show any kind of determined bias on behalf of Politifact. I don't think you really grasp what the problem is when we talk about bias in journalism. Newspapers can make mistakes. Newspapers can even report totally incorrect information. What's important is that mistakes and erroneous reporting are acknowledged, discussed, and critiqued. It's like science -- peer review is the key. When an organization like Politifact makes a claim and is then subjected to legitimate critique and then it responds to such criticism -- that is the process working. This is very different from what happens with the far-right news complex though, isn't it?