Diff Checker
Diff Checker — runs in your browser. Inputs are not stored.
Text compare (diff)
Enter values, then press Calculate.
Green is added (+), red is removed (−). Input is not sent to the server.
How to use
- Paste the old version in the left Original (A) and the new version in the right Compare (B).
- Press Compare. Common, added, and deleted lines are computed line by line.
- The stats above show same lines and added / deleted counts. Added and deleted are a combined total.
- In the result, green
+is a line only in B, red-is a line only in A, and uncolored lines are shared. - HTML special characters are escaped before display. Reset clears both sides and the result.
- Keeping original on the left and edited on the right makes green read as “new lines.” Even whitespace-only differences count as different lines.
Key concepts
Text compare (diff) aligns two documents with a line-level LCS (longest common subsequence). Shared content stays; remaining lines are deletions (red, A only) and additions (green, B only). There are no Git patch headers, word-level highlights, or moved-line detection. A single space or tab difference makes a different line, so indent-only code changes look fully rewritten.
Same-line stats are the common-line count; added/deleted is green plus red. Very long logs can slow the table, so split ranges. It fits a first-pass code review, translation proof, or config-file diff. Neither box is sent to a server. If you need character-level highlight, treat this as a draft and use an editor or Git for detail.
Example
If A is alpha / beta and B is alpha / gamma, you get 1 same line and 2 added/deleted. beta is a red deletion, gamma a green addition, alpha uncolored. Comparing two empty sides shows only an “(empty)” note. HTML tag characters are escaped so markup does not break. A single extra comment in a config file makes that whole line look changed. Matching line endings on both sides before compare reduces noise.
Related: Find and replace · Markdown preview · Character counter
Frequently asked questions
Is the text diff character-level?
It is line-level. If only a word changes inside a line, the whole line shows as a deletion plus an addition. There is no whitespace highlight.
Are lines that differ only in spaces treated as equal?
No. Different spaces, tabs, or trailing whitespace make a different line. Indent-only code can look fully changed.
How are added and deleted counts tallied?
Green lines plus red lines. Same lines are counted separately. A changed line is usually 1 deletion + 1 addition.
Can it produce a Git diff patch?
It only highlights on screen. It does not export <code>diff -u</code> headers or patch files—use Git for commits.
Can I compare very long logs?
Yes, but many lines can make LCS table work slow. Cut out the problem range.
Is the diff stored on a server?
No. Original A and compare B are matched only in the browser and are not sent or saved.
Last reviewed: 2026-09-04