What is Wordle? The game filling your Twitter feed with squares

Everyone from Marian Keyes to Richard Osman is playing it

A screenshot from Wordle

If you've been on Twitter in the last week you’ve probably noticed your newsfeed slowly filling up with weird numbers and coloured squares accompanied by the word ‘Wordle.’ 

Everyone from Irish author Marian Keyes to British Labour MP Jess Philips and Richard Osman is getting involved — but what is it and how do you play?