AI style rewriter: rewrite any draft into a measured voice

By Jack Stovell · published 2026-09-21 · updated 2026-09-20

A style rewriter only works if the style is measured first. So this one starts by measuring your sample: counting sentence length, contractions, commas, the lot, then writing the rewrite instructions in numbers rather than adjectives. Vague prompts produce vague voices. Numbers don't.

Paste a sample into the builder below (120 words or more does it) and watch it get measured in real time. It'll count the same features the paid product counts, then hand you a system prompt built entirely from your own numbers, ready to run through any assistant.

Why 'rewrite this in my style' fails

Here's the thing: "my style" isn't an instruction. It's a vibe. And large language models are bad at vibes when there's no measurement underneath them.

Ask an assistant to sound more "confident" or "punchy" and it'll guess. It might add exclamation marks. It might shorten a few sentences and call it a day. What it won't do, because it can't, is know that your writing runs 0.5 contractions per 1,000 words less than it should, or that your average sentence length needs to drop from 17 to 11.

SGR-002 tested this directly. A one-page measured prompt (asking for roughly 14 contractions per 1,000 words, formality at 3.7) got GPT-5 to obey the countable rules: no em dashes, more short sentences. But on the things that weren't spelled out as numbers, it drifted hard. It produced 0.5 contractions per 1,000 words instead of 14. Judged formality landed at 7.2, nearly double the target. The result scored 0.62 against the study profile. ScriptGrain's generation, working against the full profile rather than a static prompt, scored 0.83.

So the prompt worked, up to a point. It just wasn't the same thing as measurement continuing through the whole rewrite.

The free workflow: measure, rewrite, score

Three steps, and none of them cost anything.

1. Measure. Paste a sample of 120 words or more into the builder below. It runs in your browser, counts sentence length and variation, contractions per 1,000, punctuation rates, pronoun mix, and the judged features (formality, humour, structure) too.
2. Rewrite. The builder turns those numbers into a system prompt: not "sound casual" but "formality 3.7, contractions around 14 per 1,000, sentences under eight words for roughly a third of the total." Paste that prompt alongside your draft into any assistant.
3. Score. Run the result back through the free off-voice check. It compares two pieces with no fixed profile: 0.80 or above reads as on-voice, 0.55 to 0.79 is drifting, under 0.55 is off. It also needs 120+ words per piece, and it stores nothing.

That third step matters more than people expect. A rewrite that feels right can still measure wrong, and you won't know which until you check.

For the mechanics behind all of this, the full method sits at /reference/voice-measurement-framework.

What the paid rewrite adds

The free route gives you a prompt. That's honest, and it's useful, but a prompt is static: it doesn't watch what the model actually does with it. It fires once and hopes.

The paid tools measure the output too, then adjust.

Polish (1 credit) revises a draft toward a profile's target of 0.9, running up to three measured passes and returning the best one. Instead of one shot at matching a voice, it checks itself against the profile after each pass and course-corrects. Rewrite-page (1 credit per 1,500 words) does the same thing across a whole web page, images considered, not just the copy block. Both return before-and-after scores, so you're not guessing whether it worked.

This is the gap SGR-002 measured directly. GPT-5 with the free prompt hit 0.62 against the author's profile. ScriptGrain, scoring each pass against the full profile rather than firing a prompt and hoping, hit 0.83. The free route is a start. It isn't the ceiling.

If you want to see how a mimicked voice compares to a genuinely measured one, /tools/ai-style-mimic and /research/chatgpt-vs-a-measured-voice both go into more of the same study.

Where the line is

Rewrite into your own voice. Rewrite into a house voice you write for. Rewrite into a voice you have permission to use. Fair enough, that covers most legitimate reasons anyone wants this tool.

What it doesn't cover: a named living person's voice, without their say-so. That's not a legal disclaimer bolted on for the look of it, it's the actual boundary the tools are built around.

To be fair, most competing tools don't even raise the question. Hyperwrite's own ai-style-rewriter page, as it stood on 2026-09-20, ran 652 words with no date, no author, no example, and no evidence the rewrite matched anything. No measurement, so no way to know if it worked, and no attempt to ask whether it should.

If you're rewriting brand or organisational copy rather than personal work, /tools/brand-voice-consistency-checker is the more direct fit.

Questions

Does the free rewriter actually change anything, or just suggest tweaks?

It produces a full system prompt built from your sample's measured numbers, sentence length, contractions per 1,000, punctuation rates, judged formality and structure. You paste that prompt with your draft into any assistant, which does the actual rewriting. The builder measures; your assistant executes.

How much text do I need to paste in?

120 words minimum, for both the sample you're measuring and the off-voice check afterwards. Shorter than that and the counted features (especially sentence length variance) get unreliable. There's no upper limit, though very long samples take a little longer to process in the browser.

What's the difference between the free check and the paid score?

The free check compares two pieces against each other with no fixed profile: 0.80 and above reads on-voice, under 0.55 is off. The paid route scores against a stored profile, aiming for 0.85 to 0.95, and does it across multiple passes automatically rather than once.

Can I use this to write as someone else?

Only with permission, or if it's your own voice or a house voice you write for. Not a named living person's voice without their consent. The tool doesn't police intent beyond that, but the design assumes legitimate use: your own drafts, your team's brand voice, or a profile you've been given access to.

Why does the paid version run multiple passes instead of one?

Because a single generation, even from a well-specified prompt, drifts on the features that weren't explicitly numbered. SGR-002 found GPT-5 obeyed countable rules from a prompt but still missed contractions and formality by a wide margin. Multiple measured passes let the paid tool check itself and pick the best result rather than the first one.