Note: Report bugs and request features on Github
Q: What is Diff Viewer?
A: Diff Viewer is an iOS, iPadOS, and Mac Catalyst app that allows you to compare two text files side-by-side and see the differences between them. It highlights additions, deletions, and changes with color-coded visual indicators.
Q: How do I start comparing files?
A: You have two options: 1. Tap “View Sample” to see an example comparison with built-in sample files 2. Tap the blue “Select Left File” button and green “Select Right File” button to choose your own files
Q: Why does the app look different on iPhone vs iPad?
A: The app uses adaptive layouts:
iPhone: Three-row vertical layout with a combined single-pane diff view
iPad/Mac: Horizontal dual-pane layout with left and right files side-by-side
Q: What do the different colors mean?
A:
Green highlighting: Content that was added (exists in right file but not left)
Red highlighting: Content that was removed (exists in left file but not right)
Gray areas: Blank spaces to maintain alignment
No highlighting: Unchanged content that’s identical in both files
Q: How do I select files to compare?
A: Tap the blue button (left file) or green button (right file) to open the file picker. You can select any text file from your device.
Q: Can I delete files from within the app?
A: Yes, tap the “•••” menu next to each file button to delete the currently selected file. You’ll see a confirmation alert before deletion.
Q: Why does the app remember my files after closing?
A: Diff Viewer uses security-scoped bookmarks to maintain access to your selected files across app launches, so you don’t need to re-select them each time.
Q: What file formats are supported?
A: The app works with any text-based file that can be read as UTF-8 text. This includes .txt, .md, code files, configuration files, etc.
Q: What are the arrow buttons between the panes?
A: These are “apply change” buttons that let you copy differences from one file to the other:
Right arrow (→): Copies a removed line from the left file to the right file
Left arrow (←): Copies an added line from the right file to the left file
Q: When do the arrow buttons appear?
A: Arrow buttons only appear on lines that have differences:
Right arrows appear on red (removed) lines in the left pane
Left arrows appear on green (added) lines in the right pane
Q: What happens when I click an arrow button?
A: The line is immediately copied to the other file and both files are automatically saved. The diff view updates to reflect the change.
Q: What is the undo button?
A: The undo button (↶) appears in the top-right of each pane after you make changes. It reverts both files back to their original state when first loaded and saves them.
Q: When does the undo button appear?
A: The undo button only appears when you’ve made changes using the arrow buttons. It’s hidden when no changes have been made.
Q: How do I change the text size?
A: Use the font size buttons in the center toolbar:
A− button: Decrease font size
A+ button: Increase font size
Font size range: 8pt to 20pt
Q: What are the default font sizes?
A:
Mac Catalyst: 12pt
iPhone/iPad landscape: 12pt
iPhone/iPad portrait: 10pt
Q: How does synchronized scrolling work?
A: On iPad/Mac, when you scroll in one pane, the other pane automatically scrolls to match, keeping corresponding lines aligned.
Q: What languages are the sample files available in?
A: Sample files are available in 11 languages:
English, Spanish, German, French, Chinese (Simplified), Portuguese (Brazil/Portugal), Hindi, Indonesian, Arabic, Russian, Japanese
Q: How does the app choose which sample files to show?
A: The app automatically detects your device’s language setting and loads the appropriate sample files. If your language isn’t available, it defaults to English.
Q: Can I see line numbers?
A: Yes, line numbers are displayed on the left side of each line in a smaller monospace font.
Q: How do I navigate long files efficiently?
A: Use standard iOS/macOS scrolling gestures. On iPad/Mac, scrolling in either pane will keep both panes synchronized.
Q: What’s the best way to compare code files?
A: The app uses a monospace font that’s ideal for code. The line-by-line comparison with syntax-aware diffing makes it easy to spot changes in code structure.
Q: Can I use this app offline?
A: Yes, once files are selected and bookmarked, the app works completely offline. Sample files are built into the app.
Q: Why can’t I access a file I selected before?
A: File access may be lost due to iOS sandbox restrictions. Try re-selecting the file using the file picker buttons.
Q: The app says “Error: filename” - what does this mean?
A: This indicates the file couldn’t be read, usually due to:
File being moved or deleted
Permission/sandbox issues
File encoding problems
Q: Why don’t I see arrow buttons on iPhone?
A: Arrow buttons and the undo feature are only available on iPad and Mac due to space constraints on iPhone screens.
Q: How do I report bugs or request features?