Always Show File Extensions in Finder

One global preference makes every Finder window display extensions, so 'invoice' becomes 'invoice.pdf'.

macOSFilesFindersettingsMedium risk

Run `defaults write NSGlobalDomain AppleShowAllExtensions -bool true && killall Finder`; reverse with -bool false.

01Command

Command

$ defaults write NSGlobalDomain AppleShowAllExtensions -bool true && killall Finder

02What it does

macOS hides extensions by default, which is why two files named 'report' look identical until one turns out to be report.pages and the other report.docx. The AppleShowAllExtensions key lives in NSGlobalDomain, the domain shared by every app, so one write covers all windows and new files. killall Finder is required because Finder caches preference values at launch — windows flash once and reappear. Per-file 'hide extension' flags still win for individual files.

03Risk

RiskMedium risk

Requirementskillall Finder restarts Finder windows — they reopen to their saved state.

04Undo

Undo

$ defaults write NSGlobalDomain AppleShowAllExtensions -bool false && killall Finder

05Sources

defaults — read and write user defaults (macOS man page)
SS64 · technical · 2026-09-17
Evidence: Documents defaults write with a domain and key, and NSGlobalDomain as the global preference domain.

Last verified: 2026-09-18 · Category: System & Settings

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