Spell-check catches the wrong spelling, never the wrong word. Kind-sounding can still be the wrong thing to say.

A tool that checks the surface cannot check the meaning. Sentences can be perfectly polite and still be the wrong thing for that person at that moment, and nothing in the wording will flag it. Tone is the easy part to get right and the part people check, which is why the harder question gets skipped.

Before you send the careful message this week, read it once more asking something different. Not whether it sounds nice, but whether it is what this person needs to hear. Sometimes the answer is fewer words. Sometimes it is a phone call instead.