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Diff Checker

Updated Free mock REST & WebSocket APIs

Paste two versions of a text, or open two files, to see exactly what changed. Removed text is red and added text is green, with changed words highlighted inside each line. The comparison runs in your browser, so nothing is uploaded.

+5 lines added·−5 removed

1Dear team,1Dear team,
22
3Thanks for joining the kickoff meeting on Monday.3Thanks for joining the kickoff meeting on Tuesday.
4The launch is planned for March 3.4The launch is planned for March 10.
5Please send your feedback by Friday.5Please send your feedback by Friday.
66
7Next steps:7Next steps:
8- Finalize the design8- Finalize the design
9- Write the docs9- Test on mobile and tablet
10- Test on mobile10- Prepare the press release
1111
12Best,12Best regards,
13Sam13Sam

🔒 Compared in your browser — neither text is uploaded.

How to compare two texts

  1. Paste the original into the left box and the new version into the right, or use Open file on each side.
  2. Pick Side by side or Inline, and Lines (best for code and lists) or Words (best for prose).
  3. Turn on Ignore whitespace or Ignore case to hide differences that don't matter, such as re-indentation.
  4. Copy the result as a unified diff to paste into a code review or ticket, or download it as a .diff file you can apply with git apply or patch.

How the comparison works

The diff checker uses the Myers diff algorithm (Eugene Myers, 1986), the same one used by git diff and GNU diff. It finds the smallest set of insertions and deletions that turns the original into the new version. Lines that changed are paired up and compared again word by word, so a one-word edit in a long line is easy to find.

Reading a unified diff

--- original.txt
+++ changed.txt
@@ -3,2 +3,2 @@
-Thanks for joining the kickoff meeting on Monday.
+Thanks for joining the kickoff meeting on Tuesday.
 The launch is planned for March 3.
  • --- and +++ name the old and new file.
  • @@ -3,2 +3,2 @@ means this hunk starts at line 3 and covers 2 lines in each version.
  • Lines starting with - were removed, + were added, and a space means unchanged context (3 lines around each change by default).

Tips

  • Everything shows as changed? The files probably use different line endings (Windows CRLF vs Unix LF) or tabs vs spaces. Line endings are normalized automatically, and Ignore whitespace handles indentation.
  • Comparing prose? Use Words mode. Paragraphs re-wrapped at a different width will still line up.
  • Comparing JSON? Format both sides the same way first with the JSON formatter (sort keys on) so the diff shows only real changes.

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Frequently asked questions

Is my text and files uploaded anywhere?

No. Everything runs in your browser, so your text and files never leaves your device. Nothing is logged or stored on a server.

Can I compare two files?

Yes. Click Open file above each box to load any text file: code, CSV, JSON, Markdown, logs and so on. Files are read locally by your browser. Word and PDF files are binary, so copy their text into the boxes instead.

Is there a size limit?

There's no fixed limit. Files with tens of thousands of lines compare in well under a second. For very large, very different inputs, the tool stops refining after a couple of seconds and marks the remaining block as replaced, so the tab never freezes.

What does 'ignore whitespace' do?

Lines that differ only in spaces or tabs, like re-indented code or trailing spaces, count as equal, the same as diff -w. 'Ignore case' does the same for upper- and lowercase letters.

Can I apply the diff as a patch?

Yes. The downloaded .diff is a standard unified diff. Rename the file headers to your real paths if needed, then run patch -p0 < changes.diff or git apply changes.diff.

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