Open-source alternatives to Grammarly

Grammarly does a useful job, and it has become a lot more than a spelling checker. Pro is around £10 per member a month, so a team of five pays about £600 a year. There's also a decent free plan with basic checks.

So why look elsewhere? For most people it isn't the money. It's the nagging thought that everything you type is going off to somebody else's servers to be checked: contracts, HR emails, that awkward note to a customer.

There's really just one open-source option worth considering here, and it comes with a big "but" that I'd rather put up front.

LanguageTool

LanguageTool is an open-source style and grammar checker. Its core is on GitHub under the LGPL, and it's actively developed. You'll also know it as a commercial service, with browser add-ons and a Premium plan. Those are two different things, and the difference matters.

• The open-source part is the checker itself, which you can download and run on your own server.
• The commercial part is the hosted service, the browser add-ons and the Premium features. Those are proprietary.

What you get by self-hosting:

• Spelling, grammar and punctuation checks based on the project's rule sets.
• British English, with its own set of rules, rather than American spellings dressed up.
• Lots of other languages, which is useful if you write to customers abroad.
• Your text stays on your server. That's the whole point.
• An API on your own server, which you can call from your own software.

Running it isn't a big job, but it does need someone comfortable with a command line. You need Java 8 or later, then you unzip the download and start the server. The project's own page says it's aimed at advanced users.

A few details to get right:

• The server only listens to its own machine by default. To let a team use it, you turn on public access and put it behind a reverse proxy with HTTPS, such as nginx.
• fastText is recommended for language detection on Linux and Mac. It's not available on Windows.
• The n-gram data is optional but worthwhile. It helps catch commonly confused words, such as their and there. It's about 8 GB, it's available for English, German, French and Spanish, and it really wants a fast SSD.

Then people connect to it. The neat trick is that the free browser add-on can be pointed at your own server, in its settings, instead of the LanguageTool cloud. The add-on is proprietary, so you're running an open-source server with a closed-source front end, but your text goes only to your server. The add-on's menu labels have moved around between versions, so check the docs for yours. Safari reportedly needs HTTPS, and the Windows desktop app won't work with this setup.

Here's the "but". The self-hosted version doesn't have the AI-based rules, which are cloud-only. LanguageTool Premium adds more than 20,000 extra checks for English and six other languages, plus unlimited sentence paraphrasing and style guides. Self-hosting gets you none of that.

So be clear on what you're swapping. Grammarly Pro rewrites sentences, adjusts tone and detects plagiarism and AI-written text. Self-hosted LanguageTool tells you when you've got your spelling and grammar wrong. That's a far smaller promise, but a useful one, and it's all most people actually need.

The UK angle

I wouldn't lose sleep over this one for everyday writing. Plenty of small firms use Grammarly, and for marketing copy and routine emails, a US-based checker is fine.

It matters more if your staff are typing personal data or confidential material. A checker in the browser sees what's in the text box, so think about:

• Regulated or sensitive work. Legal, HR, health and financial text often includes personal data, and UK GDPR expects you to know who's processing it.
• Client confidentiality. If your contracts promise to keep things in-house, a third-party writing tool could be a problem, whatever its privacy policy says.

If your team falls into either group, self-hosting gives you a nice simple answer: the text doesn't leave a server you control. The hosted LanguageTool service is another option if you'd prefer an EU supplier, as the company says all its servers are in Germany. Just remember that the default add-on sends text to those servers unless you change the setting.

Honest drawbacks

• No AI rewriting. No tone adjustments, no full-sentence rewrites, no paraphrasing. This is the big one if that's what you value in Grammarly.
• Fewer checks than Premium. The extra checks are reserved for the paid service.
• The add-ons are closed source. A purist won't like it, though it doesn't change where your text goes.
• Someone has to set each person up. Every browser needs pointing at your server, and it's easy to miss one and quietly send text to the cloud.
• Other apps need thought. Grammarly works in a lot of places. Check that the tools your team really uses can reach your server.
• Good checks need disk space. Without the n-gram data you miss some things. With it, you need an SSD with 8 GB to spare.

Which one?

My pick is self-hosted LanguageTool, but only if privacy is your reason for leaving Grammarly. It gives you solid spelling and grammar checks in British English with your text staying in-house. The main drawback is that you lose the AI rewriting and premium style suggestions, and for many people those are what they're paying for.

• Sensitive text, spelling and grammar are enough: self-hosted LanguageTool.
• Happy with a hosted service, want better suggestions: LanguageTool Premium, or stay with Grammarly.
• Just want tone and rewriting help: Grammarly is honestly fine.

If you'd like checks like this built into your own software, such as a customer-facing form or a document system, the team at Dev Partners can build that as custom software.

Sources

• LanguageTool on GitHub
• LanguageTool licence
• Running a LanguageTool HTTP server
• LanguageTool n-gram data
• LanguageTool Premium
• LanguageTool API and server location
• Grammarly plans
• Grammarly Pro cost, support article