Sometimes you need to check your writing and you don't have a connection. Airplane mode, a patchy signal, a conference hotel with unusable WiFi. Or maybe you just don't want your text going anywhere.
Whatever the reason, here's what actually works for offline grammar checking on iPhone in 2026.
What iOS gives you natively
iOS has a built-in spell checker. It's on by default and works with no internet required.
You'll see it underline misspelled words in most text fields. Tap an underlined word and iOS suggests corrections. It also does autocorrect, which is aggressive by default and occasionally helpful.
What it doesn't do: grammar. iOS spell check catches "recieve" but won't notice "she don't know" or a sentence fragment. It won't suggest rewrites. It won't flag a comma splice. For typos, it's fine. For actual grammar analysis, it falls short.
There's also the system-level Writing Tools feature in iOS 18, which includes grammar checking and rewriting. It's available in supported text fields (Notes, Mail, Messages) and requires Apple Intelligence to be enabled on your device. It does work offline once the models are downloaded. But it's not available in every app, and you can't paste arbitrary text into it from outside a Writing Tools-compatible field.
How to use Proofed for offline grammar checking
Proofed is an iPhone app that does grammar checking entirely on-device. It uses Apple's Foundation Models framework, which runs local inference with no network calls.
Here's how to use it offline:
1. Download while you have a connection. The app installs the on-device AI model the first time you open it. This requires internet for the initial setup. After that, no connection needed.
2. Open the app and paste your text. Tap the text area and paste whatever you want to check. Emails, messages, documents, anything up to about 800 words at a time.
3. Tap Check. The grammar analysis runs locally on your device. You'll see results in 1-2 seconds.
4. Review and apply corrections. Errors are highlighted in the text. Tap any highlight to see the issue, the suggested fix, and a plain-language explanation of what's wrong. Tap Apply Fix or dismiss it.
5. Done. Nothing was sent anywhere. Your text stayed on your phone the whole time.
If you have a Pro subscription, you also get text rewriting and tone adjustment, both of which also run on-device.
When offline grammar checking actually matters
A few situations where this is more useful than you'd expect:
Flying. Long-haul flights are good writing time. Being able to draft and edit without airplane mode tricks or spotty satellite WiFi is genuinely useful.
Sensitive documents. If you're checking anything confidential, keeping it off cloud servers is worth thinking about. I wrote more about what actually happens when you paste text into Grammarly if that's relevant to your situation.
Spotty connectivity. Commutes, rural areas, buildings with dead zones. Cloud grammar tools that stall when the connection drops are annoying. On-device doesn't stall.
Privacy as a default. Some people just don't want their writing on someone else's servers. Offline solves that without requiring any special configuration.
Tips for writers who work on their phones
A few things that make mobile writing easier in general:
Turn off autocorrect for longer drafts. Settings > General > Keyboard > Auto-Correction. For short messages it's fine. For anything longer, it quietly changes words you didn't intend.
Use a Bluetooth keyboard. The iPhone keyboard is fine for short text but slow for anything substantial. A compact Bluetooth keyboard pairs well with a phone propped up in landscape.
Write in a plain text app first. Notes, Bear, Drafts. Then paste into Proofed to check, and paste the corrected version wherever it needs to go. Keeps the workflow clean.
Check in chunks for longer documents. Proofed handles up to around 800 words at a time. For longer documents, break it into sections. The per-section approach also helps you focus on one part at a time.
FAQ
Does iPhone have a built-in grammar checker?
iOS has a spell checker that works offline by default. Grammar checking (beyond basic spell check) is available through Writing Tools in iOS 18 on Apple Intelligence-compatible devices, but only in supported apps. For a dedicated grammar check you can run on any text, you need a third-party app.
Can I check grammar without WiFi on iPhone?
Yes, with the right app. Proofed runs entirely on-device with no internet required after the initial setup. iOS's built-in spell check also works offline, but it only catches misspellings, not grammar issues.
What grammar apps work offline on iPhone?
Proofed is built specifically for on-device grammar checking on iPhone. It uses Apple's Foundation Models to run inference locally. Most other grammar apps (Grammarly, ProWritingAid) are cloud-based and require an internet connection to function.
Does Proofed work in airplane mode?
Yes. Once you've opened the app once and the on-device model has loaded, it works in airplane mode with no connection needed.
Proofed is on the App Store. No account. No internet. Your text stays on your phone.
More on how the on-device AI works: How Apple Foundation Models actually work for grammar checking.