Show HN: Grammit – Local-only AI grammar checker (Chrome extension)

Show HN: Grammit – Local-only AI grammar checker (Chrome extension)(chromewebstore.google.com)

34 points by scottfr 263 days ago | 6 comments

Hey HN, I wanted a grammar checker that didn’t send my writing to someone's servers, so we built Grammit, a Chrome extension that runs grammar checks locally using an LLM. Your text never leaves your computer during checking.

Here’s a 2-minute overview: https://www.loom.com/share/baf501ee6cf14a919a7384128246ed67

Because it uses an LLM, it catches more than spelling and grammar. For example, it can correct some wrong statements like “The first US president was Benjamin Franklin.”

Grammit also includes an in-page writing assistant that can rephrase or draft new text. It also uses the local LLM.

We used many new web features to build this, such as:

- Chrome’s new Prompt API to talk to the local model.

- Anchor Positioning API to place the UI with minimal impact on the DOM.

- CSS Custom Highlights API for inline error marking.

- The new CSS sign() function to create CSS-driven layout with discontinuities.

Part of the fun of being early adopters of bleeding edge tech is we’re discovering new Chrome bugs (e.g., https://issues.chromium.org/issues/428354426, https://issues.chromium.org/issues/428039224).

I’d love your feedback on:

- Where the UX feels rough

- What do you think of the corrections and suggestions

Happy to answer questions about the tech or the Prompt API. Thanks for trying it out!

Chrome Web Store extension link: https://chromewebstore.google.com/detail/grammit-the-ai-gram...

kurtextrem 253 days ago |

Just stopping by to say this is great usage of the new APIs.

willwade 263 days ago |

I’ve developed a couple of fine tuned t5 grammar correction models. Is the model or training open?

scottfr 263 days ago | |

Interesting, I would love to hear how well those worked.

Grammit uses the Prompt API for the local LLM, which currently uses a version of the Gemma 3n model on Chrome.

Grammit uses prompting instead of fine-tuning or custom training. Simplified, it has a system prompt along the lines of: "Rewrite this text, correcting any grammar or spelling mistakes," combined with a prefilled conversation containing a number of examples showing an input sentence and the corrected output.

doug_life 263 days ago |

Any idea why this would not be compatible with Vivaldi 7.5.3735.66? The store says "This item is not compatible with your current Chrome version"

scottfr 263 days ago | |

I don't know if Vivaldi supports the new Prompt API [0] that Grammit uses to run the local LLM.

As far as I know, the only browsers supporting it currently are Chrome [1] and Edge [2].

[0] https://github.com/webmachinelearning/prompt-api

[1] https://developer.chrome.com/docs/extensions/ai/prompt-api

[2] https://learn.microsoft.com/en-us/microsoft-edge/web-platfor...

Disposal8433 261 days ago |

What's wrong with LibreOffice?