Text Compare Tool: How to Find Differences Between Two Texts
How Text Comparison Works
Text comparison (diffing) identifies the minimum set of changes needed to transform one text into another. The standard algorithm, the Longest Common Subsequence (LCS) algorithm, finds the longest sequence of lines (or characters) that appear in both texts in the same order, then marks everything else as added or removed.
Most diff tools work at the line level — a line is either unchanged, added, or removed. Character-level (inline) diff goes further and highlights which specific characters within a changed line are different.
How to Use the Tool
This is your baseline — the version you're comparing from. Label it mentally as 'before.'
This is your new version — what the text changed to.
The tool highlights additions in green, deletions in red, and unchanged content in normal text.
Scroll through the highlighted output to review each change. Use the change counter to see how many insertions and deletions were made.
Reading Diff Output
- Green / + lines — content that was added (present in the right/new text, not in the left/original)
- Red / - lines — content that was removed (present in the left/original, not in the right/new)
- Unchanged lines — content that appears in both texts
A modified line typically shows as a red deletion followed immediately by a green addition — the original version removed, the new version added. Character-level diff highlights the specific words or characters that changed within the line.
Use Cases
Reviewing document revisions
Compare two versions of a contract, policy document, or specification to see exactly what changed between versions — useful when track changes wasn't enabled in Word.
Comparing configuration files
Diff two versions of an appsettings.json, .env, or config file to see what settings changed between environments or deployments.
Code review without a version control system
Compare two versions of a SQL query, script, or snippet to verify what changed before deploying a hotfix.
Proofreading
Compare a document before and after editing to verify only the intended changes were made and nothing was accidentally deleted.
Detecting plagiarism
Compare two essays or articles to identify copied passages that were minimally modified.
Tips for Effective Comparison
- Normalize whitespace first — if texts differ only in indentation or trailing spaces, those differences will dominate the diff. Trim whitespace or use the ignore-whitespace option.
- Compare at the right level — for code, line-level diff is usually best. For prose, character-level diff catches word substitutions better.
- Use version control for recurring comparisons — if you're regularly comparing versions of the same file, Git or a proper diff tool (like VS Code's built-in diff, or Beyond Compare) gives you history and blame information too.
- Large files — for very large documents (10,000+ lines), browser-based diff may be slow. Use a desktop tool or command-line
difffor large file comparison.