Paraphrasing versus rewriting
Most free paraphrasers are synonym swappers. They replace words with dictionary equivalents and produce text that is technically different and noticeably worse: stilted, uneven in register, and often subtly wrong where a synonym did not quite fit.
Real rewriting works at the level of structure. It changes sentence length, voice, clause order and formality, while leaving the claims intact. That is what makes the output read as though a person wrote it, because a person did make those structural decisions.
The distinction matters most with technical, legal or academic text, where a synonym swap can quietly change meaning. "The policy may apply" and "the policy will apply" are one word apart and entirely different claims.
Choosing the right mode
Clearer and simpler targets sentence length and jargon. It is the right default for anything a non-specialist will read, and it is usually the single biggest readability improvement available.
Shorter and tighter is for cutting, not just compressing. Expect to lose roughly a third of the words. Use it on anything with a word limit, and on your own writing when it feels padded.
More formal raises register without becoming stilted. Use it for applications, official correspondence and anything addressed to a body rather than a person.
More casual removes stiffness. It is the mode for blog posts, newsletters and social copy, where formal phrasing reads as distant.
Academic register handles hedging, passive constructions and citation-friendly phrasing. It preserves the caution of the original rather than hardening it.
Fix grammar only is the conservative option. It corrects errors and leaves your voice alone, which is what you want when the writing is already good and you just need it clean.
The must-preserve field is worth using
Anything you put in the must-preserve field will be carried through unchanged. That is useful for a required phrase, a defined term, a specific figure, or a length constraint. If your text has a clause that a regulator or a client requires word for word, put it here.
This is also how you protect nuance. If your original deliberately hedges, such as "may reduce" rather than "reduces", tell the tool to preserve the hedge, because some rewrite modes will otherwise resolve it into a stronger claim.
Verify with the meaning check
Every result ends with a short note on what was preserved and, where relevant, what nuance did not survive the mode you chose. Read it. If the tool says a hedge was lost, decide whether that matters before you use the text.
The most reliable verification is to read your original and the rewrite side by side, checking only the factual claims. Structure and style are meant to change. Facts and figures are not.