Newsguard, an online tool that rates and ranks news websites for credibility and transparency, is adopting a subscription model which means it will no longer be free to use.

The US start-up launched in the UK nine months ago, assigning a “green” (pass) or “red” (fail) rating to every major news website according to how many of its nine criteria were met.

It drew controversy over its decision to give Mail Online a red rating, on a par with Russian state-backed news services RT (Russia Today) and Sputnik, but later admitted its mistake and amended it to green.