Diff Checker

Paste your original and changed text, and instantly see every added, removed, and unchanged line — no server needed.

Original

Changed

Diff output

Paste text in both panels above to see the diff…

Diff is computed using a Longest Common Subsequence algorithm entirely in your browser. No text is uploaded to any server.

Overview

Diff Checker: compare two text blocks line by line

This diff checker compares two blocks of text and shows exactly which lines were added, removed, or left unchanged. It uses a Longest Common Subsequence (LCS) algorithm — the same underlying approach that git diff, Unix diff, and code review tools use — so the result is the minimal edit needed to transform one text into the other. Added lines appear in green with a + prefix, removed lines in red with a -, and unchanged lines are shown neutrally.

The tool is useful any time you need to spot what changed between two versions of a config file, a log output, a piece of code, or any plain text. Counts for added and removed lines are shown at a glance. Everything runs locally in your browser: nothing you paste is sent to a server.

100% freeNo sign-upRuns in your browserLine-by-line diff

How to use it

1Paste the original (before) text into the left panel.
2Paste the changed (after) text into the right panel.
3The diff output updates instantly — green lines are additions, red lines are deletions.
4Check the summary badges to see how many lines were added, removed, and unchanged.

Key features

Line-by-line diff using a pure JavaScript LCS algorithm

Added lines highlighted green (+), removed lines red (−)

Counts of added, removed, and unchanged lines at a glance

Works for code, config files, log output, plain text, and more

Live updates — diff rerenders as you type

Scrollable output panel for long files

100% client-side — your text never leaves your device

Frequently asked questions

What algorithm does this diff checker use?

It uses a Longest Common Subsequence (LCS) dynamic programming algorithm, the same fundamental technique used by git diff and Unix diff. LCS finds the largest set of lines that appear in both texts in order, and derives additions and removals from the remainder.

Can I use it for code diffs?

Yes. The tool compares plain text line by line, so it works equally well for source code, configuration files, JSON, YAML, logs, or any text. It does not syntax-highlight code, but the line-level diff is accurate.

Is there a file size limit?

The tool processes up to 2 000 lines per side to keep the browser responsive. Inputs exceeding that are capped with a notice at the bottom of the diff. For larger files, consider splitting the text into sections.

Does it show word-level or character-level differences?

The current tool operates at the line level, matching the behaviour of standard diff utilities. Lines that are similar but not identical are shown as one removed line and one added line rather than being merged with inline highlights.

Diff Checker

Diff output

Diff Checker: compare two text blocks line by line

How to use it

Key features

Frequently asked questions

Related Articles & Guides

How to Compare Two Text Files Online (and Read the Differences)

Diff Checker Guide: How to Compare Text and Code

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