I post on X most days, and the pattern was always the same: hit publish, read it back, and spot the typo four seconds too late. A missing apostrophe, a doubled word, a sentence that lost its verb somewhere. Deleting and reposting costs you whatever traction the post had, and leaving it there quietly annoys you all afternoon.

This article is about the small tool I built to stop that happening. It fixes the grammar in any text field with a single tap, for free, without sending a word of your text to anyone. And it uses the latest LLM technology, which shines in grammar.

How To Start?

Install the extension, and that is genuinely it. There is no account to create, no email to hand over, no trial to start and no credit card to enter.

  1. Add to Chrome (install the free)
    PI Fix Grammar Chrome Extension.
  2. Pin it to your toolbar so you can reach the settings quickly.
  3. Start typing anywhere. The first correction downloads Chrome's
    on-device AI model (a one-time download of roughly 2 GB), and everything after
    that is instant. In most cases it already sits on your device.

What is PI Fix Grammar?

The idea is borrowed, and I am happy to admit it. On my Android phone, Google's keyboard does this small magic trick: you type something sloppy, pause for a second, and a pencil icon appears. Tap it, and your sentence comes back fixed. I love it. I use it constantly, and I miss it every single time I sit down at my Windows machine, because on the desktop there has never been anything like it.

The usual answer is Grammarly, and I could never get on with it. As an extension it never felt lightweight to me, it wants an account and a subscription before it does anything, and in my experience it caused more than its share of problems on the pages it sat on. For moving one comma in a post, that is a lot of machinery, and a lot of my writing handed to somebody else's servers.

So PI Fix Grammar is that Android trick, on the desktop: a small button that appears at the corner of whatever text field you are typing in. Tap it, and your grammar, spelling, punctuation and capitalization are corrected in place, in the same field.

The interesting part is what powers it. Chrome now ships with Gemini Nano, a small language model that lives inside the browser itself. PI Fix Grammar calls that model directly, which means:

  • It is free — there is no server to pay for, so there is nothing to
    charge you for.
  • It is private — your text never leaves your machine. Nothing is
    uploaded, logged or stored.
  • It works offline, on a plane, with no usage limits.

The model is small and it will not write your novel. But fixing a comma is exactly the kind of task a small local model is good at. Short in, short out, no opinions required.

How To Use PI Fix Grammar?

01 The Floating Button – Fix The Whole Field

Type in any text field and stop. After about two and a half seconds a small green button appears at the bottom-right corner of the field. Click it, and the whole field is corrected.

This is the one I use most, and for writing X posts it genuinely changed my day. You finish the post, pause to think about it, and the button is already sitting there at the corner of the box. One click and it is clean, no copy-pasting into another tab, no second tool, no reading it back three times and still missing the doubled word.

The button is deliberately patient. It waits until you pause, it ignores anything shorter than ten characters, and it never covers your text, it tucks itself under the bottom edge of the field, and steps aside if the site already has a button in that spot.

02 Right Click – Fix Only The Selected Text

Sometimes only one sentence in a long draft is the problem. Select it, right-click, and choose PI Fix Grammar from the menu. Only the selected text is replaced, the rest of your draft is left exactly as you wrote it.

This also works on text you cannot edit. Select something on any page, right-click, and the corrected version lands on your clipboard instead.

03 The Keyboard Shortcut

Press Alt + G. If you have text selected it fixes the selection, otherwise it fixes the whole field. If you keep the floating button switched off, this is the fastest way to work.

04 Choosing Your AI Engine

Open the extension's Options and you will see which engine is currently active, right under the engine selector. By default it is Chrome's on-device model, and for most people that is the right answer.

If your machine cannot run the local model, you can paste your own free API key from Groq, Google AI Studio or OpenRouter. All three have free tiers, so this path costs nothing either.

There is also a Measure engines button. It runs the same test sentence through every engine you have set up, shows you how long each one took and exactly what each one gave back, then makes the fastest one your default. On my machine the cloud model answered in around 100 ms and the local one in about 1.5 seconds, but that depends entirely on your hardware, which is the point of measuring rather than guessing.

Further Functions

  • It fixes mistakes, not your voice. Your tone, your language, your line
    breaks, emoji, links, @mentions, #hashtags and code snippets all survive untouched. It
    will not rewrite you into a press release.
  • Ctrl + Z works. Corrections go through the browser's own
    editing pipeline, so undo puts your original text straight back.
  • It works in real editors, not just plain boxes, but the rich
    composers used by social networks and CMS tools, and inside iframes.
  • Password fields are always ignored.
  • Switch it off per site with one click from the toolbar popup, or tune
    how long it waits and how much text it needs before offering itself.

Is It Really Free?

Yes, and it is worth explaining why, because “free” usually means “free for now”.

Tools like this normally cost money because every correction is an API call to somebody's server, and somebody has to pay for it. PI Fix Grammar runs the model inside your browser, so there is no bill to recover. No subscription, no trial, no premium tier holding the good corrections back.

End Note

PI Fix Grammar is the tool I wanted on Windows for years: the thing my phone has always done, without the account, the subscription, or the weight. It is small, it is quick, and it minds its own business.

You can add PI Fix Grammar to Chrome for free and if it saves you from a typo or two, a star in the Chrome Web Store genuinely helps other people find it.

You may also check PI Prompts where you could store your frequently used ChatGPT, Gemini and Claude prompts.