The macOS built-in spell checker is notoriously aggressive. As you type in Safari, Notes, or Mail, it constantly underlines words with angry red dots, and more infuriatingly, it often auto-corrects technical jargon or brand names into entirely different, irrelevant dictionary words. If you are a programmer writing code snippets, or a writer who intentionally uses stylized language, this constant interference destroys your productivity.
While you can right-click in most text fields and uncheck “Check Spelling While Typing,” this only disables it for that specific document or application. The very next time you open a new window, the red squiggly lines return. Apple does not provide a single, universal “Off” switch in the standard System Settings to kill the spell checker entirely across the entire operating system.
To completely eradicate spell checking globally, you must use a hidden Terminal command.
Step 1: Disable Spell Checking via Terminal
We will use the defaults command to modify the global macOS preference architecture, explicitly telling the system to set continuous spell checking to false.
- Open the Terminal app (found in Applications > Utilities, or via Spotlight search).
- Copy and paste the following command exactly as written:
defaults write -g NSAllowContinuousSpellChecking -bool false - Press Return.
(Note: The -g flag stands for “global,” meaning this rule will be applied to every single application running under your user account).
Step 2: Disable Auto-Correction (Optional but Recommended)
Even with spell checking disabled, macOS might still attempt to forcefully auto-correct words it deems misspelled. To completely lobotomize the grammar engine, you should disable auto-correction as well.
- In the Terminal, paste the following command:
defaults write -g NSAutomaticSpellingCorrectionEnabled -bool false - Press Return.
Step 3: Reboot Your Mac
Because these are global preferences that affect the core text rendering engine used by every application, the changes will not take full effect until the operating system completely restarts.
- Click the Apple logo in the top left corner of your screen.
- Select Restart…
When your Mac boots back up, the spell checker will be permanently dead. You can type obscure code, made-up slang, or complex technical terms in any native macOS application, and you will never see a red squiggly line or suffer a forced auto-correction again.
How to Restore the Spell Checker
If you realize your spelling is truly atrocious and you need the safety net back, you can easily reverse the commands.
- Open the Terminal.
- Paste the following commands, pressing Return after each:
defaults write -g NSAllowContinuousSpellChecking -bool truedefaults write -g NSAutomaticSpellingCorrectionEnabled -bool true - Restart your Mac.