File Type Defaults

Set default applications for file types on macOS using utiluti. Use when setting file type associations, changing default apps for extensions, or managing macOS file handlers.

majiayu000 Updated Sep 9, 2026 567 repo stars

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Last audited Sep 24, 2026 · commit cf815d9

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File Type Defaults

Set default applications for file types on macOS using the utiluti command-line tool.

Prerequisites

Ensure utiluti is installed:

brew install utiluti

Instructions

Recommended Approach: File-based Method

The most reliable method is to use utiluti file set with a sample file. This works even for extensions with dynamic UTIs.

Step 1: Get application bundle ID

osascript -e 'id of app "Application Name"'

Step 2: Set default using an existing file

# Use an existing file of that type (preferred)
utiluti file set /path/to/existing/file.<extension> <bundle-id>

# OR create a sample file if needed
touch /tmp/sample.<extension>
utiluti file set /tmp/sample.<extension> <bundle-id>

Example:

osascript -e 'id of app "Cursor"'
# Returns: com.todesktop.230313mzl4w4u92

# Using an existing .conf file
utiluti file set ~/.dotfiles/tmux/tmux.conf com.todesktop.230313mzl4w4u92

# Or using a temporary sample file
touch /tmp/sample.conf
utiluti file set /tmp/sample.conf com.todesktop.230313mzl4w4u92

Alternative: UTI-based Method (for well-known types)

This method works for file types with standard, non-dynamic UTIs.

Step 1: Get UTI for file extension

utiluti get-uti <extension>

Example:

utiluti get-uti txt
# Returns: public.plain-text

utiluti get-uti md
# Returns: net.daringfireball.markdown

utiluti get-uti pdf
# Returns: com.adobe.pdf

Step 2: Set default application

utiluti type set <uti> <bundle-id>

Example:

utiluti type set public.plain-text com.barebones.bbedit

Note: Some file extensions (like .conf) have dynamic UTIs (e.g., dyn.ah62d4rv4ge80g55sq2) that cannot be set using utiluti type set. Use the file-based method instead.

Finding application bundle IDs

Use osascript to find an application's bundle ID:

osascript -e 'id of app "Application Name"'

Examples:

osascript -e 'id of app "Visual Studio Code"'
# Returns: com.microsoft.VSCode

osascript -e 'id of app "BBEdit"'
# Returns: com.barebones.bbedit

osascript -e 'id of app "Preview"'
# Returns: com.apple.Preview

Common Use Cases

Configuration files (.conf) to Cursor

# Using an existing .conf file (recommended)
utiluti file set ~/.dotfiles/tmux/tmux.conf com.todesktop.230313mzl4w4u92

# Or using a temporary file
touch /tmp/sample.conf
utiluti file set /tmp/sample.conf com.todesktop.230313mzl4w4u92

Text files to BBEdit (UTI method)

utiluti get-uti txt
utiluti type set public.plain-text com.barebones.bbedit

Markdown files to Visual Studio Code (UTI method)

utiluti get-uti md
utiluti type set net.daringfireball.markdown com.microsoft.VSCode

JSON files to Cursor (UTI method)

utiluti get-uti json
utiluti type set public.json com.todesktop.230313mzl4w4u92

Python files to Cursor (file method for reliability)

touch /tmp/sample.py
utiluti file set /tmp/sample.py com.todesktop.230313mzl4w4u92

Verification

After setting a default, verify by:

Right-clicking a file of that type in Finder
Checking "Open With" → default should show your selected app

Or use command-line verification:

# For UTI-based settings
utiluti type get <uti>

# For file-based settings
utiluti file app /path/to/sample.file

Reference

utiluti GitHub: https://github.com/scriptingosx/utiluti
List of common UTIs: https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/UTIRef/Articles/System-DeclaredUniformTypeIdentifiers.html

Notes

Changes take effect immediately for new file operations
Prefer using existing files over temporary files - this ensures the exact file type is matched
Some file types may require logging out and back in for changes to fully propagate
System applications (like TextEdit) might override custom settings for certain types
When in doubt, use the file-based method - it works universally for all file extensions, including those with dynamic UTIs
The file-based method (utiluti file set) sets the association system-wide for that extension
If you still get "No application knows how to open" errors after setting the association:
- Try right-clicking the file in Finder → "Get Info" → Change "Open with:" → Click "Change All..."
- Or try opening via right-click → "Open With" → select the app
- The Launch Services database may need time to update

---name: file-type-defaultsdescription: Set default applications for file types on macOS using utiluti. Use when setting file type associations, changing default apps for extensions, or managing macOS file handlers.--- # File Type Defaults Set default applications for file types on macOS using the `utiluti` command-line tool. ## Prerequisites Ensure `utiluti` is installed: ```bash brew install utiluti ``` ## Instructions ### Recommended Approach: File-based Method The most reliable method is to use `utiluti file set` with a sample file. This works even for extensions with dynamic UTIs. #### Step 1: Get application bundle ID ```bash osascript -e 'id of app "Application Name"' ``` #### Step 2: Set default using an existing file ```bash # Use an existing file of that type (preferred) utiluti file set /path/to/existing/file.<extension> <bundle-id> # OR create a sample file if needed touch /tmp/sample.<extension> utiluti file set /tmp/sample.<extension> <bundle-id> ``` Example: ```bash osascript -e 'id of app "Cursor"' # Returns: com.todesktop.230313mzl4w4u92 # Using an existing .conf file utiluti file set ~/.dotfiles/tmux/tmux.conf com.todesktop.230313mzl4w4u92 # Or using a temporary sample file touch /tmp/sample.conf utiluti file set /tmp/sample.conf com.todesktop.230313mzl4w4u92 ``` ### Alternative: UTI-based Method (for well-known types) This method works for file types with standard, non-dynamic UTIs. #### Step 1: Get UTI for file extension ```bash utiluti get-uti <extension> ``` Example: ```bash utiluti get-uti txt # Returns: public.plain-text utiluti get-uti md # Returns: net.daringfireball.markdown utiluti get-uti pdf # Returns: com.adobe.pdf ``` #### Step 2: Set default application ```bash utiluti type set <uti> <bundle-id> ``` Example: ```bash utiluti type set public.plain-text com.barebones.bbedit ``` **Note:** Some file extensions (like `.conf`) have dynamic UTIs (e.g., `dyn.ah62d4rv4ge80g55sq2`) that cannot be set using `utiluti type set`. Use the file-based method instead. ### Finding application bundle IDs Use `osascript` to find an application's bundle ID: ```bash osascript -e 'id of app "Application Name"' ``` Examples: ```bash osascript -e 'id of app "Visual Studio Code"' # Returns: com.microsoft.VSCode osascript -e 'id of app "BBEdit"' # Returns: com.barebones.bbedit osascript -e 'id of app "Preview"' # Returns: com.apple.Preview ``` ## Common Use Cases ### Configuration files (.conf) to Cursor ```bash # Using an existing .conf file (recommended) utiluti file set ~/.dotfiles/tmux/tmux.conf com.todesktop.230313mzl4w4u92 # Or using a temporary file touch /tmp/sample.conf utiluti file set /tmp/sample.conf com.todesktop.230313mzl4w4u92 ``` ### Text files to BBEdit (UTI method) ```bash utiluti get-uti txt utiluti type set public.plain-text com.barebones.bbedit ``` ### Markdown files to Visual Studio Code (UTI method) ```bash utiluti get-uti md utiluti type set net.daringfireball.markdown com.microsoft.VSCode ``` ### JSON files to Cursor (UTI method) ```bash utiluti get-uti json utiluti type set public.json com.todesktop.230313mzl4w4u92 ``` ### Python files to Cursor (file method for reliability) ```bash touch /tmp/sample.py utiluti file set /tmp/sample.py com.todesktop.230313mzl4w4u92 ``` ## Verification After setting a default, verify by: 1. Right-clicking a file of that type in Finder 2. Checking "Open With" → default should show your selected app 3. Or use command-line verification: ```bash # For UTI-based settings utiluti type get <uti> # For file-based settings utiluti file app /path/to/sample.file ``` ## Reference - utiluti GitHub: https://github.com/scriptingosx/utiluti - List of common UTIs: https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/UTIRef/Articles/System-DeclaredUniformTypeIdentifiers.html ## Notes - Changes take effect immediately for new file operations - **Prefer using existing files over temporary files** - this ensures the exact file type is matched - Some file types may require logging out and back in for changes to fully propagate - System applications (like TextEdit) might override custom settings for certain types - **When in doubt, use the file-based method** - it works universally for all file extensions, including those with dynamic UTIs - The file-based method (`utiluti file set`) sets the association system-wide for that extension - If you still get "No application knows how to open" errors after setting the association: - Try right-clicking the file in Finder → "Get Info" → Change "Open with:" → Click "Change All..." - Or try opening via right-click → "Open With" → select the app - The Launch Services database may need time to update

majiayu000/claude-skill-registry-data/tree/main/devops/file-type-defaults commit cf815d9519

Frequently asked questions

npx skillmds@latest add majiayu000/file-type-defaults