Diff Checker

Written byOleh Soloninupdated 25 September 2026

First text

Second text

Case

Edge whitespace

Result

Differences2: − second line 2: + second line changed
Changed lines1
Matching lines2
Similarity, %66.67%
Lines in the first3
Lines in the second3

Line by line, with a similarity score

Line-by-line differences between two texts with case and whitespace options, plus a similarity percentage.

Spotting the difference between two near-identical texts by eye is close to impossible, particularly with a config file, a contract or two drafts of the same email. A line comparison does it instantly and gives the line number of every change.

The case and whitespace options matter more than they look. If the files were edited in different tools, many of the "differences" may turn out to be trailing spaces. Ignore whitespace at the ends of lines when it does not matter for the files you compare.

How to use

Paste the first version on the left and the second on the right.
Decide whether to ignore case and whitespace at the ends of lines.
Read the list of differences with line numbers, the changed and matching line counts and the similarity percentage.

How the settings change the result

The comparison goes line by line, by line number. On the left: 'first line / second line / third line' or a shorter version of it.

Every row is output from this page's checker.
What changed	Lines changed	Lines matching	Similarity
One line of three edited	1	2	66.67%
A new line inserted at the top	4	0	0%
Trailing spaces on one line, whitespace not ignored	1	1	50%
The same, whitespace ignored	0	2	100%
First letter in a different case, case ignored	0	2	100%

What this calculator shows

Every changed line with its number: minus for the old, plus for the new
How many lines changed and how many matched
A similarity percentage — the quick answer to "how different is it"

What to keep in mind

Comparison is by line number rather than by content, so inserting a line at the top shifts everything and shows as a wholesale difference.
Blank lines count like any other and affect the numbering.

FAQs

Why did inserting one line produce so many differences?

Because lines are compared by position, and an insertion shifts everything after it. A proper longest-common-subsequence diff smooths that out; this tool uses a straight line-by-line comparison.

Should I ignore whitespace?

If the files were edited in different editors, yes: trailing spaces otherwise flood the list with noise. In the table above, one such line drops similarity from 100% to 50%.

What does the similarity percentage mean?

The share of lines that match exactly, out of all lines. It does not measure how much a line changed — only whether it changed.

Is my text sent to a server?

No, the comparison runs in your browser. That matters when the texts are draft contracts or configuration files with real addresses in them.

What do the minus and plus mean?

Minus is the left-hand line, as it was; plus is the right-hand line, as it is now. Each carries its line number: '2: − second line' and '2: + second line changed'.

Why did one inserted line give 0% similarity?

After an insertion at the top, every left-hand line is compared with a right-hand line that has moved down one place, and no pair matches.

Worked example

Two drafts

Input: Three lines, the second edited

Output: 1 changed line, 66.67% similar

Note: The change is shown as a pair: first the line as it was, then as it became. That makes the actual edit easy to see.

Useful links

All tools in Text tools for word count, character count, and quick cleanup

Diff Checker

Result

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