Text Diff Checker
Compare two text blocks side by side in your browser. Line-based diff highlighted with + additions and - deletions. Uses an LCS (longest common subsequence) algorithm.
Two texts, one diff
Identical lines pass through unchanged. Lines unique to the left side are removed (-); lines unique to the right side are added (+).
The quick brown fox jumps over the lazy dog The end.
- The quick brown fox + The quick red fox - jumps over the lazy dog + jumps over the lazy cat The end. + P.S. addendum.
What you'll use this for
Anywhere two text blobs need to be compared without firing up diff on the terminal.
Contract review
Spot every clause that changed between two drafts of a legal document.
Version compare
Pre-commit sanity check — paste two versions and see exactly what shifted.
Copy editing
Show authors the precise edits applied to their drafts, line by line.
Log comparison
Compare two log outputs to find a regression or environment drift.
How to diff two texts
Paste before
Drop the original text into the left editor. Up to ~1 MB feels responsive.
Paste after
Drop the modified text into the right editor — or click Swap to flip sides.
Read the diff
Auto-compare keeps the diff fresh as you type. Lines prefixed - were removed, + were added.
Copy or download
Save as diff.txt or copy the unified-style output to your clipboard.
Frequently asked questions
Line-by-line LCS (longest common subsequence). It finds the longest sequence of unchanged lines, marking the rest as additions or deletions — the same approach used by classic Unix diff.
Yes. Two lines that differ only in case are reported as a change. If you need case-insensitive comparison, run both inputs through a text cleaner first.
Yes. Completely free, no signup, no limits. Both texts stay in your browser.
Works comfortably for files under ~1 MB. The LCS table grows as O(m × n) in lines, so very large or wildly different inputs slow down. Truncate or split first if needed.
Click the swap arrows in the After header — it flips the two sides and re-runs the diff so + and - swap roles.
About line-based text diffing
A text diff is the smallest set of edits that transforms one text into another. The LCS approach finds the longest sequence of lines present in both inputs in the same order — everything outside that sequence is an insertion or deletion.
Output format
line— unchanged context line.- line— line removed from the right side.+ line— line added on the right side.
When to use this vs other diffs
- Text diff — prose, logs, plain configs.
- Code diff — when you want language-aware syntax highlighting.
- JSON / XML / YAML diff — when whitespace or key order shouldn't count as a change.