German Grammar Checkers – A Thorough Review

Hello everyone,

and welcome back to the best German learning blog on the cyberwebs.
And today, there’s a special episode waiting for you with a fascinating look at German grammar and spell checking tools.
And what makes it super duper extra special is that the episode comes from … drumroll… one of you, the German learners.

His name is Scott Meyers and some of you might actually know him, because he is an acclaimed author of several books about the programming language C++. And I mean real, actual, “old school” books that are printed by publishers and sold in university book stores around the world.

A couple of months back, Scott reached out to me and told me about his testing of multiple German grammar checking tools, and the blog posts he had written about it.
I found that so interesting and insightful that  I asked him if he’d be open to share that with you as a guest author.
He said yes, and he didn’t just write a new article for us all, he also did multiple revisions of the article, to include new, more extensive tests and included the latest AI models that are out today (excluding OpenAI o1 Strawberry, which literally just dropped). 

I am really honored to have him as a guest author here today!
And no matter whether you’re a tech savvy person or not, the article has some insights for you for sure, and may also help you form at least part of an informed opinion about the current AI systems.

If you want to check out his blog, you can find it here:

Scott Meyers’ Blog

There are more detailed articles about his testing of grammar checkers, and all other kinds of interesting things. I found his travel tracking approach to be really cool for instance.

But now, without further ado, here’s Scott Meyers!

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(Checking out) German Grammar Checkers

(by Scott Meyers)

I work hard on my German, but I make a lot of mistakes. It’s not my fault. The language is pretty much impossible. But I want to improve, and one of the ways I try is by using German grammar checkers: programs that find and fix spelling and grammatical errors. I’ve tested a lot of them. Most are mediocre. Some are worse. A couple are pretty good. And then there are the ones on the verge of being so good, they’ll be like having your own private native-speaking tutor once they work the kinks out. In this article, I’ll give you an overview of what’s available, how well it works, and what to watch out for.

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There are two basic types of checkers. Dedicated checkers are special-purpose programs that do nothing but check for spelling and grammatical errors. They behave like English spelling and grammar checkers in word processing programs, and in fact the German-language checkers in Microsoft Word and Google Docs are two of the systems I tested. There are a number of web sites that provide similar services.

Dedicated checkers all work the same way. You type or paste in text for them to check. They highlight words or phrases they think are wrong. When you click on highlighted text, they suggest a replacement, which you accept or reject. Accepted changes are incorporated into the text, and you move on to the next error. It’s the classic word processor spell-checking experience.

The other kind of checker is “smart” AI chatbots such as ChatGPT. These programs are based on a technology known as LLMs (“large language models”), so I call them LLM chatbots. ChatGPT is probably the best-known, but there are others, including Copilot, which Microsoft is pushing so hard, it’s having PC makers put a special key on new computers for it. I tested the German grammar-checking skills of four LLM chatbots: ChatGPT, Copilot, Gemini, and Claude.

LLM chatbots can do pretty much anything you want: create recipes, summarize novels, analyze YourDailyGerman’s obsession with squirrels and unicorns–you name it. When you want them to check German for spelling and grammatical errors, you have to tell them that. Here’s what I tell them before I paste in the text I want them to proof:

“Please highlight and correct the grammatical and spelling errors in the following German text. Don’t make any stylistic changes. Just highlight and correct the errors.”

The remark about not making stylistic changes is to prevent LLM chatbots from being too helpful. I don’t want them to rewrite my text to make it sound like I’m a native speaker (which they can do). I want my text to sound like me, but with the mistakes fixed.

As for the “please” at the beginning, it’s unnecessary. I’m dealing with machines, not people. I included it, because I couldn’t stomach the militaristic-sounding, “Highlight and correct the grammatical and spelling errors in the following German text!”
A little politeness couldn’t hurt, I figured, but recent research suggests that the tone of your prompt can actually affect the results you get.

My Testing

I tested 16 spelling and grammar checkers. Links to them are at the end of this article. All are free. Most are available without creating an account. Some offer more extensive checking for users who are logged in, but I took advantage of that only in the case of ChatGPT. I also used logins to access Claude and Gemini, because there’s no other way to get at them.

My testing was done on a laptop computer running Windows.

I tested the checkers in two ways. First I had them look at the following individual sentences, each of which has an error in it (highlighted in bold):

  1. Das Tisch sieht gut aus.
  2. Ich gehe im Küche.
  3. Ich bin in die Küche.
  4. Ich will einen Ort finden, die schön aussieht.
  5. Beim Check-in haben wir die Größe des Lobbys bewundert.
  6. Schließlich habe ich mich entschlossen, dass ich einen Ort finden musste, der zwischen Singapur und den USA liegt (d.h., der auf dem Heimweg ist), und die gute Flugverbindungen hat.

Only three of the systems found and fixed the problems in all six of what I call The Sentences. The majority of the systems didn’t even find and fix the mistakes in sentences 1-3, which I’d call A1-level grammar.

You don’t usually run an English spell-checker on a single sentence. You run it on something bigger, such as an email message or a document. The same is true in German, so in addition to testing the checkers on The Sentences, I had them check some email messages I’d written and a short essay I’d composed. I call these The Documents. Nothing in The Documents was longer than about 870 words (roughly two pages). It’s a sad reflection on my German that that provided plenty of errors for the checkers to sink their teeth into.

I scored the checkers on how well they found and fixed the mistakes in The Sentences and in The Documents. Each error was worth four points: two for finding it and two for fixing it. If a checker didn’t offer a specific fix, but instead gave a list of possible fixes that included the correct one, it got half credit: one point. If it proposed only a single fix, but that was incorrect, it got penalized: -1 points for that.

Between The Sentences and The Documents, there were more than 50 errors to find and fix. Three quarters of the systems turned in embarrassing performances. Their find-and-fix scores were less than 50%. Two checkers–both LLM chatbots–broke away from the pack. Claude got a nearly-perfect 95%, while ChatGPT earned a respectable 86%.

There’s more to a good German writing aid than finding and fixing problems, however. Read on to see why I don’t use Claude or ChatGPT for my daily spelling- and grammar-checking needs.

Dedicated Checkers

I tested a dozen web sites. Only three are good enough to be useful:

  • LanguageTool, which scored 66%.
  • Scribbr and QuillBot, which are sites from sister companies that almost certainly use the same underlying checking software. They performed identically in my tests, where they earned 67%. That’s essentially the same as LanguageTool, though my subjective impression is that LanguageTool is, overall, a wee bit better.

Everybody else did so poorly (below 50%) that I’m not going to bother to show their scores:

  • Rechtschreibprüfung24 and Korrekturen performed identically on my tests, so I suspect they use the same software under the hood.
  • GermanCorrector, OnlineKorrektor, and TextGears all probably use the same checking technology, because they produced the same results on my tests. Mostly. Unlike GermanCorrector and OnlineKorrektor, TextGears limits its input to 500 characters–about 10 lines of text. This means GermanCorrector and OnlineKorrektor were able to check The Documents, but TextGears wasn’t.
  • Sapling often says only “[Sign in to see premium edit]” about text it highlights. I gave it no credit for these. Signing in would presumably improve its score, but I prefer no-login-required checkers, and that’s how I tested it.
  • Duden Mentor. The most hallowed name in the German language offers a surprisingly weak spelling and grammar checker that limits input to 500 characters and offers no fixes for the errors it finds.
  • Online-Spellcheck distinguishes itself by being the slowest of the checkers as well as offering the most cumbersome interface.
  • studi-kompass is a site I’m not sure I ever got to work, even though I tried it in three different browsers. For words it thought were misspelled, it offered both German and English replacements.

I can’t think of any reason to choose an “everybody else” site over LanguageTool and/or Scribbr/QuillBot. None of them find as many mistakes as these sites, and many of the also-rans have special drawbacks, e.g., they run slowly, have awkward user interfaces, don’t offer fixes for the errors they find, etc. The only redeeming aspect of the time I spent testing them was discovering the myriad ways it’s possible to do their job badly.

The checkers in the following word processors have scores that put them in the same league as the wannabe web sites:

  • Google Docs (32%).
  • Microsoft Word (22%). Most of my testing was done with Office 2010, but some was done with Office 365. I didn’t notice any difference in their performances.

If you’re already using these programs to compose your text, there’s no harm in taking advantage of their checking tools. Just don’t fool yourself into thinking that if they say you’re writing’s clean, it is.

The top-scoring dedicated checkers, LanguageTool and Scribbr/QuillBot, have the interesting characteristic that each tends to find errors the other misses. Running both of them, one after the other, raises their combined score to 82%. That’s not quite as high as ChatGPT’s 86%, much less Claude’s 95%, but it’s high enough that the LanguageTool+Scribbr/QuillBot approach is the one I use.
I’ll explain why below.

LLM Chatbots

LLM chatbots are under very active development, so what’s true of them today may not be true tomorrow. Over the course of two months, one LLM chatbot went from getting a perfect score on The Sentences to getting credit for only five of the six, then back to getting a perfect score again. You should view the information that follows as merely a snapshot of LLM chatbot behavior as of August 2024.

In the competition to find and fix errors, Claude and ChatGPT eat Gemini and Copilot for lunch. Look at the numbers:

  • Claude (95%)
  • ChatGPT (86%)
  • Gemini (47%)
  • Copilot (42%)

This is partially due to length restrictions. Copilot accepts inputs of up to only 2000 characters. That’s less than a page of text. Two of my Documents are longer than that, so Copilot checked only part of them. I could have broken them into pieces and checked the pieces individually, but I don’t pander to my proofreading tools.

Gemini also seems to have a length limitation, but it’s not on how much text you input, it’s on how much it outputs. It seems to be restricted to about 4600 characters. That’s less than the length of one of the Documents, so if it found errors beyond the 4600 character mark, it had no way to tell me.

Even without these limitations, Gemini and Copilot would trail Claude and ChatGPT by a notable margin. They’re just not as good at finding mistakes. Nor are they as good as LanguageTool and Scribbr/QuillBot, much less them in combination. Look:

  • Claude (95%)
  • ChatGPT (86%)
  • LanguageTool+Squibbr/Quillbot (82%)
  • Squibbr/QuillBot (67%)
  • LanguageTool (66%)
  • Gemini (47%)
  • Copilot (42%)

This means the only sweeping generalization we can make about the performance of dedicated checkers versus LLM chatbots is that we can’t make any sweeping generalizations.

The LLM ChatBot Checking Experience

If numbers were the whole story, we could quit here. Claude is astonishingly good at finding and fixing errors in German (or at least in my German), and ChatGPT isn’t far behind. I aspire to Claude’s German skills!

But numbers aren’t everything, and once you go beyond them, there’s good news and bad news. The good news is that when an LLM chatbot finds and fixes an error in German, you can ask it to describe what was wrong and how the revised text resolves it. This is something dedicated checkers can’t do, and when you get an LLM chatbot on a good day, you’ll think you’re dealing with one of the best language tutors in the world. For example, The Documents include this:

Da ich schon zweimal in Singapur war, möchte ich dieses Mal Singapur
als ein Zwischenstopp auf dem Weg nach Nordwestaustralien behandeln.
(Because I’ve already been to Singapore twice, this time I’d like to treat
Singapore as a stopover on the way to northwest Australia.)

Claude changed “als ein Zwischenstopp” to “als einen Zwischenstopp.” I asked for an explanation. It said:

“als ein Zwischenstopp” → “als einen Zwischenstopp” “Als” requires the accusative case here.

I wasn’t satisfied. “Please explain in more detail,” I said. Claude replied:

  1. In German, “als” can be followed by either the nominative or accusative case, depending on its function in the sentence.
  2. When “als” is used to express a comparison of equality (meaning “as” or “like”), it’s typically followed by the same case as the noun it’s being compared to.
  3. However, in this sentence, “als” is being used in a different way. It’s part of the construction “etwas als etwas behandeln” (to treat something as something).
  4. In this type of construction, where “als” is used with verbs like “behandeln” (to treat), “bezeichnen” (to designate), or “betrachten” (to regard), it requires the accusative case.
  5. “Zwischenstopp” is a masculine noun. In the accusative case, the indefinite article “ein” changes to “einen” for masculine nouns.

Therefore, the correct form is “als einen Zwischenstopp”.

That’s impressive, especially the nicely generalized “etwas als etwas behandeln.” But not all days are good for LLM chatbots. When I asked Claude why it’s das Verdachtsmoment, even though it’s der Moment, Claude said,

The word “Verdachtsmoment” is a compound noun made up of:

“Verdacht” (suspicion) – which is masculine
“Moment” (moment) – which is also masculine

Since the core or main noun in the compound is“Moment”,
which is masculine, the entire compound noun “Verdachtsmoment”
takes on the masculine gender.

Uh huh. Except that “Verdachtsmoment” is neuter, not masculine. Sigh.

ChatGPT got “Verdachtsmoment” right, pointing out that there are two German nouns spelled “Moment”, one of which is neuter, and that’s the one that’s the basis for “Verdachtsmoment“. But ChatGPT has bad days, too. It once tried to convince me that “während dieser Monate” is in the dative. (It’s not. It’s genitive.)

Copilot and Gemini offer similarly schizophrenic behavior.

I’m confident that further work on LLM chatbots will improve their reliability, but for now, we’re stuck with the fact that when they’re good, they’re really, really good, but when they’re bad, they’re terrible. That’s a problem. One of the things I want in my grammar-checking tools is reliability.

Something else I’m looking for is an easy way to see what an LLM chatbot has flagged as incorrect. Look again at the instructions I gave the LLM chatbots:

Please highlight and correct the grammatical and spelling errors in the following German text.
Don’t make any stylistic changes. Just highlight and correct the errors.

“Highlight” is a word with some wiggle room, but Claude’s interpretation was to put square brackets around a single character it decided needed to be eliminated. Does it jump out at you in the context in which it occurs? (The context looks strange, because I asked Claude to check some unrelated sentences, but please ignore that.)

Wie du vermutlich schon gesehen hast, habe ich das dem Typ in der Storageanlage vorgeschlagen. Wenn es Probleme gibt, sag mir bitte einfach Bescheid. Überraschenderweise gibt es fast keine. Mitte[l] März habe ich angefangen, von Windows auf macOS umzusteigen, eine Aufgabe, die ich für eine Dauer von etwa sechs Wochen eingeschätzt habe.

This is Claude’s way of highlighting that “Mittel März” should be “Mitte März“.

Not that Claude is wedded to square bracket highlighting. Another time it used the most subtle boldfaced text I’d ever encountered. I had to increase the page magnification to see it.

Claude’s terrible highlighting contrasts with its outstanding ability to find and fix errors. The result is a system that’s extraordinarily good at finding and fixing mistakes, yet extraordinarily bad at showing you what it’s done.

I could have told the LLMs how I wanted them to highlight their changes (e.g., in a special color), but I didn’t get that far. There was a bigger problem. I had trouble getting the LLM chatbots to reliably highlight their changes at all. Sometimes they did, and sometimes they didn’t, and often they highlighted some changes and didn’t highlight others. There didn’t seem to be any rhyme or reason to it. On one occasion, whether highlighting was visible depended on the width of my browser window! This highlighting inconsistency turned what should have been a trivial task–reviewing everything that was changed–into hard work.

I don’t need proofing tools to make my life harder. I have German for that.

My Approach

The ideal German spelling and grammar checker is simple, fast, reliable, and accurate. Claude and ChatGPT take the prize for accuracy, but using them is neither fast nor simple. You have to tell them what to do, and you have to work to see what they did. Their reliability is unproven. They may be the future, and it’s interesting to experiment with them, but as checkers for German spelling and grammar, they’re not yet ready for their close-ups.

Dedicated checkers are simple and fast. It’s a pity that most of them aren’t very good. LanguageTool and Scribbr/QuillBot are exceptions. Type or paste in your text, accept or reject each of the changes they propose, then copy the revised text and paste it where you want it (e.g., email, WhatsApp, document, etc.). Their accuracy rate is high enough that you can be confident that most of your spelling and grammatical errors have been fixed.

With a bit of additional effort, you can up their accuracy rate to about that of  ChatGPT. After copying your corrected text out of one of the checkers, paste it into the other one. Accept or reject the changes that are proposed, then copy the result and paste it where you want it. This is what I do. I keep browser tabs with LanguageTool and Scribbr open, so when I need to check some German, they’re sitting there waiting for me. I often use one or both to check my outgoing messages in WhatsApp. Composing the messages takes longer than checking them, so passing my texts through LanguageTool and/or Scribbr improves my German without interrupting the flow.

Dedicated Checkers:

LLM Chatbots:

 

Scott Meyers has been working on his German since 1977. He blogs on random topics at https://scottmeyers.blogspot.com/, where he published the posts from which this article emerged.

 

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And that’s it!!
I’m really curious for your thoughts about this topic. Do you use grammar checkers to check your German writing?
Which ones do you use and why? Are there any that were not part of the article today?
Let me… or actually let us know in the comments, so I’ll see you there.
Or I’ll see you next week with a new article :).
In either case, I really hope you enjoyed this one, and thanks again to Scott for doing this.
Have a great week and bis zum nächsten Mal.

Oh, here’s the link again, if you want to dig deeper:

Scott Meyers’ Blog 

 

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