Free Writing Checker
Paste an email, essay, post, or message and get practical style flags in your browser. This offline writing checker highlights passive voice, filler and vague words, adverbs, long sentences, repeated words, double spaces, common word confusions, and readability — without pretending a simple rule engine can replace a full grammar editor. Nothing you paste leaves your device.
Want the actual fix, not just the flag?
Synapse rewrites the sentence for you inside any app. Select your text, tap a prompt, and get a cleaner version without switching to a website.
See the AI grammar checker keyboard →This is an offline writing and style checker, not a full grammar corrector. Nothing you type is uploaded.
What the checker can and cannot do
The checker looks for patterns that are often worth a second read: a passive construction that hides the actor, a filler phrase that adds words without meaning, a sentence that has become difficult to scan, or a common confusion such as your and you're. It does not know your audience, your facts, or your intent, so every flag is a suggestion rather than an automatic correction. A passive voice can be the right choice; an adverb can be exactly what you mean.
Readability is a guide, not a grade
Flesch Reading Ease estimates how easy a passage is to read from its sentence length and syllable count. Flesch–Kincaid estimates the school grade level needed to follow it. Both are useful when you are writing for a broad audience, but they are not quality scores. A technical explanation may need longer words; a short message can be clear even when its score is unusual. Use the numbers to spot a mismatch between your draft and your audience, then make the call yourself.
From a flag to an actual rewrite
A browser checker is useful when you are polishing a draft, but it still makes you copy the text out of the app where you are writing. The Synapse AI grammar checker keyboard works in the opposite direction: select the sentence in WhatsApp, Gmail, LinkedIn, or another Android app, tap Fix Grammar, and review the rewrite without switching contexts. It is the actual fix after this page has shown you where to look.
Private by design
There is no API call behind this tool. The rules, readability math, highlighting, and copy action all run locally. Your draft uses the same browser-only storage pattern as the other Synapse tools, so a refresh does not erase work in progress; clearing site data removes it.
Frequently Asked Questions
What does this writing checker find?
It checks for common style problems: passive voice, filler and vague words, adverb overuse, sentences longer than 25 words, repeated words, double spaces, missing capitals after sentence punctuation, and commonly confused word pairs such as your/you’re and its/it’s. It also calculates Flesch readability and a Flesch–Kincaid grade estimate.
Is this a full grammar checker?
No. It is an honest offline writing and style checker, not a complete grammar corrector. It flags patterns that are often worth reviewing, but it cannot understand your full meaning or guarantee that a suggestion is right. Read every suggestion before changing your text.
Is my writing uploaded?
No. The checks run in your browser with JavaScript. Your draft is saved in this browser only so you can return to it; it is not sent to a server or used to train anything.
What is a good readability score?
A Flesch Reading Ease score from 60 to 70 is generally plain English for a broad audience. Technical, academic, or legal writing can reasonably score lower. Readability is a guide, not a quality grade: clarity and accuracy matter more than chasing a number.
How can Synapse fix the flagged writing?
The Synapse AI keyboard rewrites selected text inside WhatsApp, Gmail, LinkedIn, and other Android apps. Select the sentence, tap a prompt such as Fix Grammar or Make Shorter, and review the rewritten version where you are already typing.
Is the writing checker free?
Yes. It is free, has no sign-up, and runs locally in your browser with no AI call or usage limit.