Diff Checker
Paste two versions of a text side by side and see exactly what changed, line by line. Everything runs in your browser — nothing you paste is sent anywhere.
What is a diff, and when would you use one?
A "diff" (short for difference) is a line-by-line comparison of two versions of a text. Instead of reading both documents in full and hoping to spot every change, a diff highlights only the lines that differ — added lines in green, removed lines in red. It is how programmers have reviewed code changes for decades, but it is just as useful outside of code:
| Situation | What the diff tells you |
|---|---|
| Contract revisions | Exactly which clauses the other party changed before you sign |
| Essay or article drafts | What an editor (or you, last Tuesday) rewrote between versions |
| Emails and announcements | How the final sent version differs from the draft you approved |
| Code and configuration files | Which lines changed between two copies of a file |
| Terms of service updates | What actually changed in that "we've updated our policy" notice |
How to read the + and − notation
This tool uses the classic unified-diff convention. Each line of the result starts with one of three markers:
− (minus, red background) — the line exists in the Original but not in the Changed text. It was removed or rewritten.
+ (plus, green background) — the line exists in the Changed text but not in the Original. It was added or is the new wording.
No marker — the line is identical in both versions. Long stretches of unchanged lines are collapsed into a gray "… N unchanged lines …" row so the changes stand out.
When a sentence is edited, you will typically see it as a red (old) line immediately followed by a green (new) line — read the pair together to see what was reworded.
When the diff says everything changed and the text looks identical
This is the most common confusing result any comparison tool produces, and the cause is almost never in the words. It is in the characters you cannot see.
- Line endings. Windows ends a line with two characters, a carriage return and a line feed (CRLF); Unix, Linux and macOS use one (LF). That carriage return sits invisibly at the end of every single line. Compare a file saved on Windows against the same file saved on a Mac and every line differs, while both panes look identical on screen. This page detects the mismatch and says so before you go hunting for a change that is not there.
- Trailing spaces and tabs. A space at the end of a line, or an indent switched from tabs to spaces, is a real change to every tool that reads the file and no change at all to your eye. This page counts the differences where the characters match and only the spacing moved, and reports them separately.
If line endings are the problem in a codebase rather than a one-off comparison, the durable fix is a .gitattributes file that normalises them on commit — not a manual conversion that will drift back the next time someone opens the file in a different editor.
Sources
- Git —
gitattributesdocumentation — thetextandeolattributes that normalise line endings across platforms, which is the fix for the CRLF/LF problem described above rather than a workaround for it.
Frequently asked questions
Is my text uploaded or stored anywhere?
No. The comparison runs entirely in your browser using JavaScript. Nothing you paste is sent to any server, which makes it safe for contracts and other sensitive documents.
Is the comparison case- and whitespace-sensitive?
Yes. "Hello" and "hello" are treated as different lines, and so are lines that differ only in spacing or tabs. If two lines look identical but show as changed, check for trailing spaces or a tab-versus-space difference.
Is there a size limit?
The tool comfortably handles a few thousand lines per side. To keep your browser responsive, texts longer than 5,000 lines on either side are not compared — split very large files into sections instead.
Does it detect changes within a line?
The comparison works line by line: an edited line is shown as one removed line plus one added line, rather than highlighting individual words. For most documents that is enough to spot the change at a glance.