Short answer: compare the rewrite with your original in a fixed order. First the hard facts (numbers, dates, names, direct quotes), then the claims (negations, hedges, cause and effect), then the references. Use a side-by-side or highlighted-changes view, read the figures out loud against the source, and never trust a rewrite you haven’t checked, however good it sounds.
AI rewriting tools are good at style and occasionally careless with substance. A model that’s been asked to “vary the sentences” may round “47.6%” to “almost half”, turn “Dr Okafor” into “the researcher”, or merge two quotes into one smooth sentence. None of these slips is dramatic on its own. In a report, an essay or a client document, any of them can be the one thing a reader notices.
This guide is a checklist you can run on any rewrite, from any tool: paraphrasers, humanizers, translation tools or a chatbot you asked to “make this sound better”.
Why facts drift in a rewrite
A language model doesn’t copy your text and then edit it. It reads it and generates a new text that’s statistically likely to express the same content in the requested style. Most of the time that works. But generation optimises for fluent, plausible sentences, and a few kinds of detail are easy to lose along the way:
- Precise figures sound clunky, so they get rounded or turned into words (“roughly a third”).
- Names get replaced with descriptions (“the minister”, “a leading study”) to avoid repetition.
- Quotes get paraphrased, because the instruction was to change the wording, and the model doesn’t always treat quotation marks as a boundary.
- Hedges (“may”, “suggests”, “in this sample”) get dropped because confident sentences read more smoothly.
- Negations and comparisons occasionally flip, especially in long sentences with “not only… but”, “less likely” or double negatives.
The pattern is consistent: the rewrite gets smoother and the detail gets vaguer. That’s why checking is about the specific, not the general.
The 7-step fact check
Run these steps in order. Each one targets a different kind of slip, and doing them separately is faster than trying to spot everything in one read-through.
- Open both versions side by side. Don’t check from memory. Put the original and the rewrite next to each other, or use a tool view that highlights what was added and removed. Highlighted changes show you where to look; a clean result hides it.
- List every number in the original. Percentages, amounts, years, dates, sample sizes, page numbers, version numbers. Find each one in the rewrite. It should appear with the same value and the same unit. “12 participants” and “a dozen participants” are equal; “12%” and “about 10%” are not.
- List every proper name. People, organisations, places, products, laws, theories named after someone. Check the spelling too. A rewrite that replaces “the Smith (2021) model” with “a recent model” has lost both the name and the citation.
- Check every direct quote word for word. Text in quotation marks must be identical to the source, including word order. If the rewrite changed a quote, put the original back. If it turned a quote into a paraphrase, decide whether that’s acceptable and keep the citation either way.
- Read each claim for strength. Look for the words that set how strong a claim is: “may”, “might”, “suggests”, “is associated with”, “in some cases”, “most”, “some”. Compare them with the original. “Suggests a link” becoming “proves” is a factual change, not a style change.
- Check direction and logic. Negations (“not”, “no longer”), comparisons (“more than”, “less likely”) and cause and effect (“because”, “led to”). Read the sentence and ask: does it still say the same thing happened, in the same direction, for the same reason?
- Check references and links last. Every citation in the original should still be there and still attached to the right claim. If a rewrite introduced a new source you didn’t have, treat it as suspect until you’ve found and read it. Language models can produce references that look real and don’t exist, a risk the MLA Style Center explicitly warns about when you use generative AI.
What a slip looks like in practice
| Original | Rewrite | What went wrong |
|---|---|---|
| “Sales rose 47.6% in Q3 2025.” | “Sales rose by almost half last autumn.” | Figure rounded, quarter replaced with a season |
| “Dr Okafor’s team tested 214 samples.” | “The researchers tested over 200 samples.” | Name dropped, exact count lost |
| “The data suggest a possible link.” | “The data show a clear link.” | Hedge removed, claim strengthened |
| “Not all respondents agreed.” | “The respondents did not agree.” | “Some disagreed” became “all disagreed” |
| She called it “a modest but real improvement”. | She called it a small yet genuine improvement. | Direct quote reworded and quotation marks lost |
These examples are illustrative, not taken from any particular tool. The point is the shape of the error: every rewrite in the middle column is fluent, grammatical and wrong.
Ways to make checking faster
Mark the untouchables before you rewrite
Before you paste a text into any rewriting tool, skim it and note the figures, names and quotes. Five seconds of highlighting gives you a checklist for later.
Rewrite smaller chunks
A paragraph is easier to check than a chapter. Shorter inputs also give the model less room to reorganise content, which is where facts tend to move.
Use your editor’s search
Searching the rewrite for each number from your list (“47.6”, “214”, “2025”) is quicker than reading. If the search finds nothing, you’ve found a slip.
Read numbers aloud
Transposed digits (“1,250” vs “1,520”) are easy to miss by eye and easy to catch when you say both versions out loud.
Ask for another version, not a patch
If a rewrite got several facts wrong, regenerating is often faster than fixing it line by line. Then check the new version from step 1. A new version isn’t automatically more accurate.
What automatic checks can and can’t catch
Some tools now run an automatic comparison after rewriting. humai does this for the AI humanizer and the paraphrasing tool: it checks that numbers (including the digits in dates), proper names and direct quotes from your original still appear in the result. If something seems to be missing, it can retry the rewrite, and if the problem remains it shows a note asking you to check numbers and names before you use the text. You can also switch to a view that highlights what changed compared with your original.
That catches the most common slips. It can’t catch everything:
- A hedge that disappeared (“suggests” → “shows”) contains no number and no name.
- A flipped negation keeps all the same words in a different order.
- A figure attached to the wrong claim still appears in the text, so a presence check passes.
- Names at the start of a sentence, or ordinary words used as names, are hard to tell apart from regular capitalised words.
So treat an automatic check as a first filter. Steps 5 and 6 of the checklist (strength and direction of claims) are always on you. The same goes for the proofreader: it corrects spelling, including the spelling of names, so it’s deliberately not run through the same name check. Compare the highlighted corrections with what you meant.
A note on AI scores
If you’re checking a rewrite, you may also be looking at an AI-style score, either in a humanizer or in a separate AI detector. Keep the two questions apart. A score is an estimate of how machine-like the style is, not proof of who wrote the text, and it says nothing about whether the facts are right. A text can score as perfectly “human” and still contain a wrong number. Accuracy is something only a comparison with your source can confirm. For the research on how reliable detector scores are, see do AI detectors actually work?.
Quick summary
- Rewrites tend to make details vaguer, not just different.
- Check in a fixed order: numbers, names, quotes, claim strength, direction, references.
- Use a highlighted-changes view and your editor’s search.
- Automatic checks catch missing figures and names, not changed meaning.
- You’re responsible for the final text, whichever tool produced it.
If you’re choosing a tool in the first place, our comparison of a paraphraser, a humanizer and a proofreader explains which one changes the least for your situation. And if you’d like to see how a rewrite handles your own figures, try a paragraph in the free humanizer and compare the two versions with the checklist above.