Why does iPhone underline words that are spelled correctly?
Check Spelling is a third switch, separate from Auto-Correction — it flags anything missing from a fixed dictionary, so a name, a brand, slang or a word from another language gets a red squiggle even though nothing about it is actually wrong.
You type a name, a brand, a word borrowed from another language — something you are certain is right — and a red squiggle appears underneath it anyway, the same mark iOS uses for an actual typo. It reads like the phone is telling you that you got something wrong. Nothing did. The word failed a specific, narrow check, and once you know what that check is actually doing, the red line stops feeling like an accusation.
A third switch, not Auto-Correction acting up
Settings → General → Keyboard holds three related switches that get lumped together in most people’s heads: Auto-Correction, Predictive, and Check Spelling. The first two are covered elsewhere — Auto-Correction silently swaps a word it thinks you mistyped, Predictive runs the QuickType suggestion bar. Check Spelling is the third one, and it does neither of those things. It never changes a single character of what you typed. All it does is draw a red squiggly line under a word it does not recognise, and stop there.
That is worth sitting with for a second: turning off Auto-Correction does not touch this. A red squiggle after you have switched Auto-Correction off is not the phone quietly turning itself back on — it is Check Spelling, working exactly as designed, on a completely separate switch.
What “misspelled” means to this particular check
Check Spelling is not judging whether a word is correct in any general sense. It is comparing what you typed against a fixed dictionary and flagging anything that is not a close match to an entry in it. A word can be spelled perfectly and still get the red line, for the simple reason that it was never going to be in that dictionary to begin with. The check has no way to know that — it only knows whether a match exists.
The words it flags most
- Names and surnames, especially ones that are not common English given names.
- Brand names and product names — plenty of real companies spell their name in a way no dictionary would recognise on purpose.
- Internet slang, texting abbreviations, and deliberately casual spellings.
- Technical terms, code identifiers, and jargon specific to a field.
- A word from another language, dropped into an otherwise single-language sentence.
Why a word from another language sets it off
Each keyboard you add in Settings carries its own dictionary, tied to its own language, and iOS swaps the whole correction and checking stack the moment you switch keyboards. That is convenient once you are actually switched over — but it also means the dictionary behind Check Spelling only ever knows one language at a time. Type a correctly spelled French word while the English keyboard is active and there is nothing in that dictionary for it to match, so it gets flagged, not because the word is wrong but because the active keyboard was never carrying a dictionary that included it. Switch to the matching keyboard and the same word passes without comment.
It quiets down for words you actually use
iOS keeps a personal, learned vocabulary on top of its base dictionary — words it has seen you type and stick with often enough to treat as genuine. A name or a piece of slang that gets flagged today can stop getting flagged after you have typed it repeatedly and never corrected it, once it has earned a place in that learned list. There is no toggle for this and no visible progress bar; it happens quietly in the background as a side effect of how you actually type.
That learned list can also be cleared, which resets this along with it: Settings → General → Transfer or Reset iPhone → Reset → Reset Keyboard Dictionary wipes the learned words and nothing else — no photos, no apps, no accounts. Do that and any name or slang word that had stopped getting underlined will start getting flagged again until it earns its way back in.
Turning it off entirely
- Open Settings → General → Keyboard.
- Find the switch labelled Check Spelling and turn it off.
That removes the red squiggle everywhere, for every kind of word — the names and brands that were never going to match a dictionary, and the genuine typos it would otherwise have caught. It is a reasonable trade if you write a lot of proper nouns, code or a second language and find the constant underlining more distracting than useful; just know it is an all-or-nothing switch, not something you can scope to specific words.
It is not something a keyboard draws
Auto-Correction and Predictive, as covered elsewhere, are things Apple’s own keyboard implements — a third-party keyboard replaces both with its own logic instead of reading those two switches. The red squiggle behaves differently: it belongs to the text field itself rather than to whichever keyboard happens to be drawing the keys underneath it, which is why the same underline shows up under an unfamiliar word regardless of which keyboard, Apple’s or a third-party one, was used to type it.
Where Kibo fits
Kibo does not touch Check Spelling at all — it runs its own separate word suggestions and Damerau-Levenshtein autocorrect from a settings panel on the keyboard itself, with common words weighted forward and up to 12 candidates you scroll through sideways. None of that reads or writes the system dictionary Check Spelling relies on, so the red squiggle behaves exactly the same whether you are typing on Kibo or on Apple’s own keyboard, and none of it needs Full Access. Kibo is free to download.
Frequently asked questions
Does turning off Check Spelling also turn off Auto-Correction?
No. They are independent switches in Settings → General → Keyboard. Check Spelling only underlines words it does not recognise; Auto-Correction silently swaps them. Turning off one leaves the other exactly as it was.
Why does a name I type all the time still get underlined?
iOS builds a personal vocabulary from words you type and keep, but a word only earns a place in it after you have used it repeatedly without correcting it. Missing that consistently, or having recently reset the keyboard dictionary, both delay it.
Does a third-party keyboard show the same red squiggle?
Yes. Check Spelling is applied to the text field itself rather than drawn by whichever keyboard is active, so the same underline appears under an unrecognised word no matter which keyboard, Apple’s or a third-party one, typed it.
Try it on your own keyboard
Kibo is a free custom keyboard for iPhone with real mechanical key sounds, a wardrobe of themes and RGB backlight effects. No account, no ads, and it works with Full Access left off.