Rewriting text with AI: which tool for which purpose

This article is an overview based on vendor information, documentation and publicly available reporting, not a scored test of our own. Prices and features change quickly; the vendor's own terms always take precedence. We only score what we have used ourselves for weeks: those tools are listed under AI tools compared.

Rewriting is not one task

Behind the wish to rewrite a text with AI lie four different tasks. The first is polishing: typos, clumsy sentences, repeated words. The second is a change of tone, from an internal note to a customer email, from informal to formal address. The third is shortening and simplifying, and the fourth is completely reformulating a text with the same content.

For the first two tasks, specialised tools have the edge: they change only what they are meant to change and show every edit. The last two need more language understanding than a proofreading tool brings; this is where chatbots play to their strength, with the risk that they change more of the substance than asked.

DeepL Write: the specialist for tone and style

DeepL, ranked first in our AI translation & writing tools category, offers a dedicated rephrasing tool in Write. It knows four styles, simple, business, academic and casual, and four tones, enthusiastic, friendly, confident and diplomatic. For German there is also a switch between formal and informal address that turns a "du" email into a "Sie" email without touching the rest.

Individual words or whole sentences can be replaced with alternatives in one click, long paragraphs shortened, and a list of protected terms stops product names or technical terms from being "improved". Without an account, 1,500 characters per pass are possible, 2,000 with a regular DeepL Pro subscription. It only becomes unlimited with Write Pro, available as an add-on for 6.99 euros per user per month on annual billing; it is included in the Business plan.

A plus for business use: according to DeepL, texts in Write Pro are not stored as long as you are signed in, and are not used for training on any Pro plan. Write works in eleven languages and is available as an extension in Word, Google Docs and Gmail.

LanguageTool, Grammarly, Duden and QuillBot

LanguageTool, founded in Potsdam and part of the American company Learneo since 2023, rephrases sentences in five modes: general, formal, concise, fluent and simple. Without a subscription you get three rephrasings a day, with Premium they are unlimited. Since early 2026 the browser extension can only be used with a subscription after a trial; the website and the LibreOffice integration remain free.

Grammarly has handled German since September 2025, but rewriting whole paragraphs is part of the paid plan. The company renamed itself Superhuman in November 2025; the product is still called Grammarly. Duden, the German dictionary publisher, also offers AI rephrasing and tone adjustment in its writing assistant, formerly Duden Mentor, with servers in Germany and a promise not to use texts for training. QuillBot, a sister of LanguageTool, rephrases up to 125 words at a time in two modes on its free plan.

All four are strong on spelling, grammar and sentence structure, and they show changes visibly. On the question of whether a paragraph is needed at all, they do not help.

Chatbots: more flexible, but more checking

An assistant such as Claude, ChatGPT or Le Chat, which Mistral now runs under the name Vibe, can do everything the specialists can and more: turn a technical text into plain language, bring a press release down to 600 characters, suggest three versions with different attitudes. In our test Claude produced the cleanest German prose with the fewest stock phrases.

The price is control. Chatbots like to change more than asked, smooth over deliberately chosen terms or add statements that were not in the original. A clear instruction helps: "Make the following email more polite. Keep all facts, figures and dates. Do not change the content, and at the end list every change in substance." It still does not replace comparing the original with the new version.

If you already work in Microsoft 365 or Google Workspace, rewriting is available right in the document: "Rewrite with Copilot" in Word and "Help me write" in Google Docs both work in German, each with a suitable plan. For notes and wiki pages, Notion AI offers the same function in its editor.

Rewriting is not an invisibility cloak

One misconception is stubborn: that a text rephrased with AI passes as your own work as long as no detection software finds it. German courts see it differently. In February 2026 the Administrative Court of Kassel upheld a failed exam for AI-based cheating and held that a single undisclosed use can be enough. The cheating was not proven with software but with contradictions between the written work and the oral exam. In June 2026 the Administrative Court of Cologne accepted invented sources as sufficient proof.

AI detectors are unsuitable for this anyway. A 2023 study of fourteen tools found them unreliable overall; they recognised rephrased AI texts in only about a quarter of cases, while falsely flagging human texts. Several universities therefore advise against using them; why is explained in our article on AI detectors.

Outside universities too: anyone who has someone else's protected text rewritten in order to publish it as their own creates an adaptation, which under copyright law requires the author's consent as long as it still recognisably follows the original. Rewriting improves your own text; it does not turn someone else's into yours.

Data protection: what may go into the input box

The texts that get rewritten are often exactly those containing personal data: customer emails, appraisals, complaints. On ChatGPT's free plans, training use is switched on by default; at Claude it has depended on a switch in the settings since autumn 2025. DeepL Pro and the Duden writing assistant exclude training according to their own statements.

For work texts, the same rule therefore applies as for any AI tool: a plan with a data processing agreement, training switched off, names replaced beforehand if in doubt. The checklist is in our article on GDPR and the AI Act.

Which tool for which purpose

For business correspondence in German, changes of tone and form of address, DeepL Write is the most precise tool. For spelling and grammar in long documents, LanguageTool or the Duden writing assistant do more, because they check the whole text instead of rewriting it.

For anything beyond polishing, such as simplifying, restructuring or versions for different readers, a chatbot is the better choice, with a clear instruction and a look at the result. In practice the combination works well: rebuild the draft in the chatbot, fine-tune it in DeepL Write. Which other office tasks pay off this way is shown in our article on AI applications in the office.

In short: DeepL Write for tone, style and formal address in German, LanguageTool and Duden for correctness in long texts, a chatbot such as Claude or ChatGPT for simplifying and restructuring. Rewriting does not make AI use in exams permissible, nor does it turn someone else's text into your own.