You wrote it, so you hear it in the tone you meant. They will hear it in the tone they are already in.
That is the whole gap, and it is why re-reading it yourself 10 times does not help.
Free to try. We never store your chats.
"It's fine" is 2 words and it can mean 4 different things. Which one it means depends on what came before it and who is saying it.
A tone checker that only looks at the sentence is guessing. It has to know what normal looks like for this person before it can tell you that something is off.
Length, against your normal. A short reply from someone who always writes short is nothing. From someone who does not, it is the whole message.
What you left out. Not answering 1 of 2 questions is a choice and it reads as one.
Timing. The same sentence at 2am carries weight it does not carry at lunch.
The version of this that is actually useful runs before you hit send, on your own draft, and tells you which line is doing damage.
Afterwards it is just an explanation of why it went badly.
Paste what they sent and it tells you how it reads. Paste what you were about to send and it tells you how that will read to them — then cleans it up without making it sound like somebody else.
We never store your chats.
Try it on your conversation