Text Diff Checker
Compare two texts and see exactly which lines were added or removed. Side-by-side, colour-coded and instantly readable.
How diff works
A diff algorithm finds the longest common subsequence between two texts — the largest set of lines that appear in both, in the same order. Everything left over is either an addition or a deletion.
This matters because a naive line-by-line comparison produces noisy output. Change one line in the middle of a paragraph and a naive diff flags every subsequent line as changed. The LCS approach correctly identifies that only one line actually differs.
Reading the output
- Red lines (
-) were removed from the original - Green lines (
+) were added in the new version - Unmarked lines are identical and shown for context
Common uses
- Reviewing a revision before sending it
- Checking whether a config file changed
- Comparing a generated output against a template
- Spotting a subtle edit in a contract or changelog
Tip
For large files, diff on the command line gives you more control:
diff -u original.txt modified.txtAdd --color=always for readable output and -w to ignore whitespace-only changes.
Frequently asked questions
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser.
How does it decide which lines changed?
It finds the longest common subsequence between the two texts, then reports everything left over as added or removed. This avoids flagging every line after a small edit.
Can it compare files?
Paste the contents of both files into the two fields. For very large files, the diff -u command is considerably faster.
Does it ignore whitespace?
No, whitespace differences are reported. Run diff -w on the command line if you want to ignore them.
Is it case-sensitive?
Yes. Hello and hello are treated as different lines.