Despite the .us domain, the operation is Sydney-based, so there’s a proper Australian spelling option. On a trial run through my personal site, it quickly picked up a bunch of stupid errors, which (as a pedant of long standing) I’m now kicking myself for lasting this long without being detected. With that said, it also inevitably picked up a lot of individual names and specialised vocabulary. You can add frequently used terms to an individual dictionary.
spellr.us is free to trial and for a quick once-over on your site, though it gets costlier pretty quickly if you want ongoing checking, with the cheapest option costing $24 a month. That’s probably too pricey for your personal site, but could be a worthwhile investment on a business site with a lot of text content that changes regularly.