I think that a spelling widget within Kagi similar to that which DuckDuckGo has would be beneficial. This would be useful for times when you don't remember if a certain word is spelled one way or the other. Or possibly for words you don't use often enough to fully memorize the correct spelling:
Spelled Incorrectly
Spelled Correctly
This widget would likely be triggered by phrases like "how to spell X" or "correct spelling for Y". It would likely be similar to that of DuckDuckGo by showing whether the word you gave it is a valid/existing word and suggestions for similar words whether it is right or wrong. When clicked a suggestion would probably define the suggestion you selected.
Preferably, the spacing/readability would be better than the DuckDuckGo version. This could be similar to the definition widget as shown by this rough "concept":
