Spelling and grammar check for your thesis and studies

Reviewed by Benjamin Lohrer, editor at corrected.eu · Last updated: 3 August 2026

Which grammar check is worth using? We tested it

Looking for a grammar check? This page shows what automatic tools do well for spelling, grammar and punctuation, where they fail, and how our own test of four well-known tools turned out. There is also a five-error quiz in English, and a short section on what is different in German.

Want to try it straight away? Grammar check online with AI

Our grammar check test: the tools that took part

• MS Word autocorrect
• Duden spell checker
• ChatGPT 3.5
• DeepL Write AI assistant

We tested well-known tools with tricky quizzes that we wrote ourselves. Want a whole text checked? Compare the results here, or use our free AI proofreader.

Date of the test: 17 March 2024

Grammar check: advantages and disadvantages

Before the results, here is a short summary of what grammar AI can and cannot do.

On the whole, AI grammar correction has become quite good at spelling, grammar and punctuation. But as of 17 March 2024, even the best AI could not match the level of a professional editor, who works with a maximum error rate of 3 per cent.

On more demanding levels such as sentence structure, textual logic, breaks in style or pragmatic nuance, grammar tools reach their limits.

How the test with 122 error cases came about

On 17 March 2024, the same prepared corpus of 122 error cases was run through the tools compared. We recorded how many errors each tool detected and how many wrong corrections it added. The results are a dated snapshot, not a lasting ranking of today's product versions.

• Constant input: an identical error corpus for every tool.
• Two measures: errors detected and wrong corrections.
• Limit: style, sources, argumentation and current product updates were not measured.

The test corpus consisted of German-language error cases, so the figures show how the tools cope with German text. Editorial review on 3 August 2026: Benjamin Lohrer, B.A. in Linguistics.

Grammar quiz: can you find all 5 errors?

We fed this quiz and others into the various AI tools. This English version has five errors (the original quiz in our test was German). Test your own proofreading skills:

Test results: the ranking

All figures come from the 17 March 2024 test described above.

• Microsoft Word: contains an AI-based autocorrect that finds and marks errors in spelling, grammar and punctuation, but only in part.
• Duden spell checker: the Duden offers a free online spell checker for German.
• DeepL Write: the DeepL Write assistant claims to be the best in the world.
• ChatGPT: the world-famous AI does well in the grammar check.
• Professional editors: editing by online providers is not free, but as of 2024 trained professionals leave the AI looking dated. With a usual error rate of at most 3 per cent, they stay ahead of the AI.

What a grammar checker is

A grammar checker is a program that goes through a text for errors in sentence structure: wrong cases, missing commas, a tense that does not fit the sentence. The words grammar checker, grammar check and grammar correction describe the same work from different angles.

A grammar checker reliably finds what can be described with rules. It reaches its limit with a sentence that is grammatically correct but says something other than what was meant. The 122-case test above shows how far the programs carry today.

For a term paper, a job application or a book, the same order applies: run the grammar checker first, then read the text yourself, and for important texts finish with an edit by a professional. Each stage finds what the previous one misses.

Common grammar errors in English theses

• comma splices and run-on sentences (two main clauses joined by only a comma)
• subject-verb agreement in long sentences ("The results of the study ... is")
• inconsistent tense, for example switching between past and present when reporting sources
• its and it's, their, there and they're, affect and effect
• dangling modifiers ("Having read the paper, the conclusion was clear")
• mixing registers, for example contractions in a formal academic text

For commas, see our page on comma rules.

How German grammar differs

If you write or edit German texts, or translate between the two languages, these are the points where German grammar needs different checks.

• Capitalised nouns. Every noun in German starts with a capital letter. A tool that treats Arbeit as a possible error because it is capitalised is simply wrong.
• Cases and gender. German has four cases and three grammatical genders. Article and adjective endings must agree, and the agreement can break in long sentences. English has nothing comparable, so English tools do not check it.
• Verb position. The finite verb stands in second position in a main clause and at the end of a subordinate clause: Er sagt, dass er kommt. ("He says that he is coming.")
• Commas before subordinate clauses. German always puts a comma before dass and before relative clauses. See our page on comma rules for the details.
• Compound words. German writes many compounds as one word, and the choice between one word and two is a typical spelling trap. Our original German quiz tested exactly these cases: zurzeit (at the moment), währenddessen (meanwhile) and aufrechterhalten (to maintain) are written as one word.
• Forms of address. German distinguishes du and Sie. Switching between the two within one academic text is a common error.

Having your grammar professionally checked

Whether you need proofreading or a full edit, our editors check grammar, sentence structure and expression more thoroughly than any AI. Billing is per standard page of 1,800 characters including spaces. Proofreading costs €1.90 per standard page, editing €4.90 per standard page. The minimum order value is €19. We work on English and German texts alike. See English proofreading and proofreading and editing for details.

Accepting corrections in Word

Our editors use Track Changes in Microsoft Word. In the Review tab you can accept, reject or comment on every grammar correction individually.

Education and studies

Anyone studying at a college or university is constantly confronted with writing. Students dig into their subjects, develop their own arguments and record the results in term papers, bachelor theses, master theses or dissertations. Academic texts like these must be sound in content, correct in language and logically structured.

The way from the first piece of research to the finished text is long and demanding. After hours of work on wording and footnotes, the concentration for a last thorough read-through is often missing. Typing errors, grammatical inconsistencies or missing commas then go unnoticed. A professional proofread or edit remedies the weaknesses reliably.

In an academic context, clean source work and a comprehensible structure are especially important. A thorough check before submission often makes the decisive difference.