I’ve been using LanguageTool for a very long time. Unfortunately, there is no longer a free tier for their Firefox add-on. From their announcement: “We have made the difficult decision to limit the use of LanguageTool’s browser extension to Premium users only.”

Some people claimed the extension becomes Premium-only starting January 16. Some others said it would be March 31. For me, the extension worked through August 15!

Now, LanguageTool still works in Basic mode (basic grammar) in their online editor, but this requires intensive copy-paste sessions. And LanguageTool, at least with a free (Basic) account, has become increasingly stupid lately, even in English. Premium costs €60/year when paid annually, or €100 for 2 years (prices vary by location).

What alternatives are worth exploring?

🤡

❶ Quillbot doesn’t offer a Firefox add-on, although it supports Chrome, Edge, Safari, and probably anything Chromium-based (Brave, Opera, Vivaldi). It covers English, French, German, Spanish, Portuguese, and Dutch. I don’t even have a free account with them, for I was disappointed by their despising of Firefox. I can’t even tell how thorough their grammar checker is because free accounts only get a basic grammar checker, just as is the case with LanguageTool. At €100/year if paid annually, that’s quite expensive. Subjectively, I like the version of Futura used for their logo, but is their grammar checker worth the money? (OK, with Premium you also get AI tools, but I’m not that interested.)

❷ Everyone in the States is using Grammarly, which never impressed me much. It does have a free Firefox add-on. Pro is €12/month if paid annually (hence, €144). Quarterly, €60. Monthly, €30. I should try the spelling and grammar checker available in the free version, just to learn why so many American students are using Grammarly’s AI to create essays.

While originally it only supported English, Grammarly now boasts grammar writing guidance in 24 languages (see also the FAQ here): Czech, Danish, Dutch, English (American and British), Finnish, French, German, Hindi, Hungarian, Indonesian, Italian, Korean, Norwegian, Polish, Portuguese (Brazil and Portugal), Romanian, Slovak, Spanish (Argentina, Mexico, and Spain), Swedish, Tagalog, Turkish, Ukrainian, Vietnamese, Chinese.

I need to give it a try.

❸ Then, Harper is a completely free grammar checker that runs fully locally in your browser. It also has a Firefox add-on, among many other integrations. The only supported language is “21st Century English” 🤡

❹ Other options exist, such as WProofreader, which has an unspecified daily word limit for free accounts, and it costs €34/month or €340/year. It supports 20+ languages, with AI-driven engines for English, German, and Spanish. No way.

🤡

After a very quick test in English, I gathered such thoughts:

  • LanguageTool’s editor didn’t catch all my grammar errors (but I was expecting that).
  • Grammarly caught all grammar errors that I was aware of, and it also had legitimate clarity suggestions. Unfortunately, not only were the tiny rephrasings Pro-only, but even a grammar suggestion required Pro! Argh.
  • There is a flaw in Grammarly that sometimes prevents it from identifying a mistake in a sentence that is buried in a lengthy paragraph.
  • Quillbot was equally good with grammar, but it insisted on the Oxford comma (LanguageTool does it, too). We’ll see later that it has some quirks, though.
  • Harper was simply dumb, missing most grammar errors 🙁 Its spelling checker flagged almost all proper nouns, plus the “argh” interjection.

So it’s between Grammarly (24 languages) and Quillbot (6 languages, and more expensive). It looks like Grammarly has an edge, eh?

Nuances: 

  • Quillbot accepted “LanguageTool still works in the Basic mode (basic grammar) in their online editor” and only corrected “Basic” to “basic” (I used “Basic” as the name for the free plan), just like LanguageTool did. In the full paragraph, Grammarly suggested removing the “the” before “Basic” for clarity, but not if the sentence was used alone, when it corrected an agreement instead: “in its online editor.” 
  • Grammarly was the only one to replace “became increasingly stupid lately” with “has become increasingly stupid lately.”
  • Quillbot missed correcting “as it’s the case” into “as is the case.”
  • Correcting “Quillbot missed to correct” into “Quillbot missed correcting” is free in Quillbot, but Pro in Grammarly. But after Quillbot changed “to correct” into “correcting,” it underlined “missed correcting” as a candidate for a premium clarity suggestion! If it’s not optimal, why did it correct it in the first place?
  • Grammarly corrected “there is no free tier anymore” into “there is no longer a free tier.” Everyone else missed it!
  • Grammarly corrected “Quillbot” to “QuillBot,” although the official spelling is now “Quillbot.”
  • In some cases, Quillbot insists on inserting a space after a period before the closing quotation marks, like this: “ending. ” Strange bug, and extremely annoying!

I suppose Grammarly is a winner, especially if one pays for it. Too many suggestions, both regarding grammar and clarity, require a paid account. But it’s not exactly cheap.

🤡

Gemini came up with some extra suggestions:

❺ The self-hosted LanguageTool open-source server. To this, I objected that the official statement that “LanguageTool’s core functionality is open source. Anyone can set up their own LanguageTool server.” does not mean that this core functionality includes the entire set of grammar-checking capabilities! And even the online correction is of questionable quality lately. It’s not even consistent, as I explained in The most retarded AI failure is LanguageTool, not the chatbots.

Gemini agreed: “If you spin up languagetool-server.jar locally, you are only getting the raw XML rule engine. You do not get the Premium neural models, you do not get the advanced context-aware checks, and you are still at the mercy of its rigid, baseline Java parser. It will be deterministic, yes, but it will be consistently basic. It won’t catch the nuances that Grammarly caught in your tests.”

❻ DeepL Write, which I never tried. Gemini claims that beyond the translator, DeepL also includes “an exceptionally capable AI-driven writing assistant,” and that the official DeepL Firefox add-on includes DeepL Write functionality. It listed English (US/UK), German, French, Spanish, Italian, and Portuguese as supported languages, and it concluded, “The free tier is remarkably generous for daily use.”

When I asked about using it in WordPress’s Gutenberg editor, Gemini tracked back: “Technically yes, it works, but practically, it might drive you crazy. Because you are dealing with WordPress’s Gutenberg editor, you are going to run into the classic React Virtual DOM conflict.” To cut a long story short, right after a correction by DeepL Write, Gutenberg’s React engine would throw the famous dreaded error: “This block contains unexpected or invalid content. Attempt block recovery.” (Using a “Classic” block inside Gutenberg, meaning the old TinyMCE editor, works, though.)

❼ Antidote, a product that I have known since 1997, when it only knew French, and when I started using it to replace Le Correcteur 101 (which I liked a lot; here’s what it looked like). Meanwhile, Antidote also corrects English, but since version 11, it has unfortunately discontinued its Linux edition.

Apparently, purchasing a per-device perpetual license of Antidote 12 is restricted to organizations (a minimum of five licenses is required just to get a quote), and individuals are forced into the subscription model: Antidote+ Personal English and French is €89/year, or €59/year for one language. Antidote+ includes Antidote 12, Antidote Web, and Antidote Mobile. They have completely walled off the buy-it-once model.

Otherwise, to avoid correcting the text in a separate window, Antidote 12 includes a Correction Express mode that performs inline correction in any web editor. The good news is that it has fixed the previously notorious incompatibility with WordPress’s Gutenberg block editor.

To correct the text in a browser, the Connectix agent can be configured to use the local Antidote 12 installation instead of Antidote Web, which sends the text to a remote server. Using the local engine will open an Antidote 12 window, but the corrections will be mirrored in the web editor, including Gutenberg. Obviously, Linux users are restricted to Antidote Web. On the other hand, users of the (cough, cough) cracked edition for Windows cannot use Antidote Web, so the browser add-on should interact with the local binary via Connectix to make the add-on work.

Antidote is highly customizable concerning what it tolerates in each of the two supported languages, but it tolerates a somewhat liberal use of English by default:

  • It always accepts a comma before “but.”
  • It doesn’t enforce the Oxford comma, but it defaults to accepting a comma before the coordinating conjunction in lists of three or more items.
  • It also always accepts a comma before “and” when “and” separates sentences.
  • A funny default in English is to allow the omitted comma in “Hello Paul!”
  • For “other commas,” there is a slider with three positions, but it’s not obvious what it requires, rejects, or accepts. (I suppose it goes from accepting “In the morning I went to work” to enforcing “In the morning, I went to work.”)
  • Also, while the option to “correct the position of the period or comma relative to the closing quotation mark” is correctly set for American English to place the period or comma before the closing quotation mark (I know, I know, it’s illogical, especially if you’re a software developer or a mathematician), I couldn’t find an option to correct the obviously wrong forcing of the placement of the period before the closing round bracket when this ends the sentence and should be placed after the closing parenthesis!

On the other hand, Antidote surprised me by not accepting “it tolerates a quite liberal use of English” and insisting on “it tolerates quite a liberal use of English.” Grammarly never corrects this, probably because it perceives a distinct semantic nuance: the first one means “a rather liberal” or “a fairly liberal.”

Antidote also never flags the situations where a zero article is to be preferred (“Linux users are restricted to Antidote Web” is better than “the Linux users are restricted to Antidote Web”). But Quillbot behaves just the same. Grammarly does the opposite: it requires “Antidote also never flags situations where…” This is maddening! IMO, “Linux users” is truly generic, whereas “the situations where a zero article is to be preferred” points to very specific situations, so I cannot agree with Grammarly.

All in all, Antidote is somewhat disappointing for English… but so is Grammarly!

❽ ProWritingAid, which happens to have a Firefox add-on. But it only supports English, and the free tier is limited to 2 runs of 500 words per day! Subscriptions run at $120 (Premium) or $144 (Premium Pro) per year, and there are one-time payments for a lifetime license: $399 and $699, respectively. (OMG!) Over my dead body.

🤡

I need to win the lottery.

🤡

Oh, wait, I forgot! At some point, Gemini advised against “Grammarly’s bloated extension,” so I asked it what is bloated about Grammarly.

Here’s its full answer:

When software developers and sysadmins call the Grammarly extension “bloated,” they aren’t just talking about the annoying pop-ups. They are referring to its underlying architecture. Grammarly is essentially a highly aggressive, constantly polling background application shoved into a browser tab.

Here is exactly what makes its extension technically bloated:

1. Hostile DOM Manipulation and Polling

To draw those signature red and blue underlines, Grammarly doesn’t just use a lightweight CSS overlay. It fundamentally alters the HTML of the page you are on.

  • Wrapper Injection: It wraps your text fragments in its own custom HTML nodes to apply styling. This actively pollutes the text field’s DOM, which is exactly why it notoriously crashes state-driven web apps like WordPress Gutenberg or React-based editors.
  • Aggressive Polling loops: Because it needs to know if the text moved (if you scrolled or resized the window), the extension runs constant background polling—checking the text field coordinates every second or so, bypassing native, lighter-weight methods like IntersectionObserver.
  • Keypress Interception: It attaches event listeners to intercept every single keystroke before it appears on the screen, adding an estimated 17–22 milliseconds of input delay per character. On long documents, this creates a deeply frustrating typing lag.

2. Massive Resource Drain (CPU & Memory)

For a tool that is supposed to just check text, its background footprint is notoriously heavy.

  • The Idle RAM Tax: Even when you aren’t actively typing, the Grammarly extension maintains a persistent Resident Set Size (RSS) footprint of around 90–120 MB in the browser. It essentially runs a massive JavaScript bundle inside the V8 engine at all times.
  • Killing CPU Idle States: Because of the constant background polling and continuous synchronization with its cloud servers, Grammarly prevents modern CPUs from entering deep sleep states (like C10). On a Linux laptop, this constant background “chatter” measurably increases idle power draw and drains the battery, simply because the processor is never allowed to fully rest.

3. The Generative AI Feature Creep

Grammarly used to be a strict NLP grammar checker. Recently, they pivoted hard into Generative AI (“GrammarlyGO”).

Even if you only want it to check for a missing comma (and as you noted, you aren’t interested in its AI tools), the extension still forces your browser to load all the heavy UI modules, floating widgets, and background scripts required to power its generative essay-writing features, tone detectors, and phrasing sliders. You are paying the performance cost for an entire AI suite just to run a basic spellcheck.

The TL;DR: Grammarly doesn’t just quietly wait for you to make a mistake. It injects code into your webpage, intercepts every keystroke, constantly polls your screen coordinates, pings a remote server, and holds ~100MB of RAM hostage—all while trying to sell you an AI essay writer you don’t want.

For someone who specifically curates a lightweight desktop environment and disables background indexing services, running the Grammarly extension is essentially inviting the exact kind of bloated, over-engineered software you intentionally avoid right into your browser.

Gemini knows too much about me, that’s for sure! OTOH, there are also yellow underlines in Grammarly.