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Diff Checker

Compare two texts line by line with unified output or a side by side view.

Original text

Changed text

Added: — · Removed: — · Unchanged: —

Result

—
A longest common subsequence keeps unchanged blocks aligned and never marks a line twice.

How to use the Diff Checker

  1. Paste the original text on the left and the changed text on the right.
  2. Choose the unified diff or the side by side view.
  3. Read the added and removed counts, then copy the diff if you need it.

Features

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Frequently Asked Questions

Common questions about the free online diff checker.

It computes a longest common subsequence of the two line lists, then walks it to mark each line as unchanged, removed or added.
Added counts the lines only in the changed text, removed counts the lines only in the original, and unchanged counts the shared lines.
The @@ -a,b +c,d @@ line that opens each block of changes and states where a copy of that block starts in each version.
It is easier for spotting small edits in long lines, because removed and added lines are paired in two columns.
No. This tool compares whole lines, which matches how source code and configuration files are usually reviewed.
Up to eight hundred lines per side. Longer inputs are truncated so the browser stays responsive, and a note says so.
No. The comparison runs entirely in your browser, so neither text leaves your device.
Yes, the diff checker is completely free and unlimited, with no account required.

Last updated: October 10, 2026