Yarn substitution

When I do crochet, I get quite a few free patterns from various sites online, however these are often sponsored by particular brands or suppliers and I can’t always source the same yarn especially if it’s a North American site rather than a European one.
I generally get around this by looking up the specified yarn on the manufacturer’s website, getting the length of yarn per ball and finding a similar yarn that my local shop stocks that I like. This is generally ok but can be a bit of a hassle. However today I discovered that somebody clever has made a site that does the substitute for you!
Yarnsub is the site - I’m not sure if they have all manufacturers covered but at least it will give you a good place to start. Hope this is helpful!