How to use it
- Paste the Original text in the left box.
- Paste the Changed text in the right box. The result updates as you type.
- Choose Lines to compare line by line, or Words to compare word by word.
- Tick Ignore upper and lower case or Ignore extra spaces and line breaks if those differences do not matter to you.
How the differences are found
The tool finds the fewest insertions and deletions that turn the original text into the changed text. This is the longest common subsequence problem, and the method used here is the O(ND) algorithm that Eugene W. Myers published in 1986, where N and M are the lengths of the two texts and D is the number of changes.
Each line, or each word separated by spaces, is one unit. A unit that is only in the original is shown as removed; a unit that is only in the changed text is shown as added.
- A line that moved to another place shows as removed where it was and added where it is now.
- Units that are the same are shown once, in their place, without a sign.
Case and spacing options
With Ignore upper and lower case on, Apple and apple count as the same. The rule follows the language of the page: in Turkish the capital I becomes dotless ı and the dotted İ becomes i, so Işık and ışık are the same word there but not on the English page.
With Ignore extra spaces and line breaks on, a run of spaces or tabs counts as one space, and spaces at the start or end of a line are ignored. The result still shows the text you pasted.
Limits
- Each text can have up to 20,000 lines or words.
- Up to 3,000 insertions and deletions can be shown. A pair of texts that differ in more places is refused with a message.
Worked example: a short letter
The original has three lines and the changed text has three too. The first line became Hello there world, the third line became Fourth line, and the second line did not change.
The result shows 2 added, 2 removed and 1 unchanged. The removed line is shown before the added line that replaces it, so each change reads in one place.
| Result | Line |
|---|---|
| Removed | Hello world |
| Added | Hello there world |
| Unchanged | Second line |
| Removed | Third line |
| Added | Fourth line |
Frequently asked questions
Are my texts uploaded anywhere?
No. The comparison runs in your browser, and the page never sends or stores what you paste. You can check this by turning off your internet connection after the page has loaded and comparing again.
Why does a moved line show as both removed and added?
The texts are compared in their order. A line that moved is a removal at its old place and an addition at its new place, because the tool does not look for moves. The same happens in most diff tools.
What is the difference between comparing lines and comparing words?
Comparing lines marks whole lines as changed, which suits code, lists and letters. Comparing words marks single words, so a change inside a sentence shows only the words that changed.
Why is there a limit on the size of the texts?
Each text can have up to 20,000 lines or words, and up to 3,000 insertions and deletions can be shown. Beyond that a phone would become slow or run out of memory, so the tool stops with a message instead.
Does the case option work for Turkish letters?
Yes. On the Turkish page the capital I becomes dotless ı and the dotted İ becomes i, which is the Turkish rule. So Işık and ışık match when case is ignored, while on the English page they do not.
Sources
- Wikipedia: Diff (the longest common subsequence method and Myers' 1986 algorithm)
- Unicode SpecialCasing.txt (the Turkish upper and lower case rules)
Figures and text last checked on Tuesday, November 10, 2026.