[mironathetin]

"For example, if I use the same word ten times in the same paragraph, this tool would replace it by synonyms;"

Very funny. This would make terrible prose, I guess. It is part of the art to say things only once and thus make repetitions unnecessary.

[Jtsummers]

Repetition is useful for memory. If your aim is conversational, like this, it's unnecessary. But if you're telling a story, it's useful. Besides, the GP wants to reduce the literal repetition by replacing the identical words with synonyms. This is akin to writing in Inform 7 or similar interactive fiction systems. Or if, like me, you're terrible at coming up with character names, you can use <PROTAGONIST>, <ANTAGONIST>, etc. throughout while you're making outlines and such. GP would want to do something like that, with proper substitution of the name with other identifiers later on (full, partial, first, last, pronoun, nickname).

[lmm]

Makes me think of The Eye of Argon. Stygian cloud of charcoal ebony etc.