I think it should have 2 letters only: かっこいい.
I just checked the readings with "Edit in JMdict". There is only かっこいい. So could it be a displaying error?
yea probably error.
Although if you google it with that spelling, there are 600,000 hits, I guess people use it sometimes to spell out an exaggerated slangy pronunciation? I wouldn't think that's a reason to spell it that way in the entry though, otherwise there's be exaggerated pronunciations for everything. You get 76 million hits with the right spelling.
It's a display error. I will fix as part of the new site.
I'm not happy with my previous answer. Of course Jisho should never show the wrong readings. I just deployed a fix for this.
Why does its pronunciation have 3 letters い?
Is it a mistake? Or can this word somehow be pronounced like that?