Text Diff Checker Compare two texts side by side and see differences highlighted.
Text Diff Checker
Compare two texts side by side and see differences highlighted.
Enter Original Text
Paste the original text in the left input area.
Enter Modified Text
Paste the modified version in the right input area.
View Differences
See additions, deletions, and unchanged lines highlighted in the diff output below.
What Is Text Diff Checker?
A text diff checker compares two versions of text and highlights the differences between them. It uses a line-by-line diff algorithm to identify added lines (shown in green), removed lines (shown in red), and unchanged lines. This is the same type of comparison used in version control systems like Git. The tool shows a unified diff view with statistics on how many lines were added, removed, and left unchanged, making it easy to understand exactly what changed between two versions of any text document.
Why Use Text Diff Checker?
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Visual highlighting of additions, deletions, and unchanged content
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Line-by-line comparison with unified diff view
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Statistics showing total added, removed, and unchanged lines
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Copy the diff output for sharing or documentation
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Powered by the same algorithm used in Git and other VCS tools
Common Use Cases
Code Review
Compare code changes before committing to identify unintended modifications.
Document Revision
Track changes between document versions to see what was edited, added, or removed.
Contract Comparison
Spot edits in legal or business documents by placing versions side by side.
Configuration Audit
Identify discrepancies between configuration files across staging, testing, and production environments.
Technical Guide
The diff checker uses the Myers diff algorithm (via the "diff" npm library) to compute the minimum set of changes needed to transform one text into another. It operates on a line-by-line basis, producing a list of change objects that indicate whether each segment was added, removed, or unchanged. The algorithm has O(ND) complexity where N is the total length and D is the number of differences, making it efficient for texts with few changes. The output is rendered with color-coded highlighting: green background for added lines, red background with strikethrough for removed lines, and muted color for unchanged context lines. Each line is prefixed with +, -, or space to indicate its change type.
Tips & Best Practices
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1Paste both versions at once for instant comparison — no button needed
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2The diff is computed line by line, so even small changes highlight the entire line
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3Use the Copy Diff button to share changes with colleagues
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4For character-level diffing within lines, consider using a dedicated code diff tool
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5The tool handles large texts but may slow down with tens of thousands of lines
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📝 Text ToolsFrequently Asked Questions
Q What algorithm does a text diff checker use?
Q Does a text diff tool compare characters or lines?
Q Can I compare code files with a text diff checker?
Q What do the colors in a diff comparison mean?
Q Is there a size limit for online text diff comparison?
About This Tool
Text Diff Checker is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.