The question is never whether they differ
You already suspect they do. The question is what changed, and most comparison tools do not answer it: they mark a line red and the same line green and leave you to find the altered word yourself. On a contract clause of forty words that is exactly the job you opened a tool to avoid.
So every edited line here is compared again word by word, and only the words that actually moved are marked. One number changed in a long sentence shows up as one number.
The worst case is when nothing visible changed at all
Two lines look identical on screen and refuse to match. It is maddening, it wastes ten minutes every time, and it is always one of a short list of characters that render the same as an ordinary one:
- A non-breaking space. Word inserts one when it does not want a line to wrap, and copying out of a web page brings them along.
- A curly apostrophe or quotation mark. Word substitutes these as you type, so "don't" from a document and "don't" from your keyboard are different strings.
- An en or em dash where a plain hyphen is expected. Autocorrect does this without telling you.
- A zero-width character. No width, no appearance, carried out of a web page. It is genuinely invisible.
- A tab standing in for a run of spaces.
- A trailing space at the end of a line, which nothing on screen shows.
When a changed line looks identical, this tool says so, names the character, says which side has it, and marks the position with a visible stand-in. That is the reason to compare in a tool rather than by eye, and it is the thing the big comparison sites do not do.
A moved paragraph is not a deletion and an insertion
Cut a clause from page one, paste it on page three, and a plain diff shows a large red block and a large green block. Nothing was edited, but the comparison reads as though the document was rewritten, and you end up checking both blocks line by line to satisfy yourself that they match.
Here, a line that disappears from one place and reappears unchanged in another is reported as a move, with the line number it went to. That is usually the single biggest reduction in what you have to read.
Leave the options off the first time
Ignoring spacing makes a comparison tidier and it also hides every one of the invisible characters above. That is fine once you know they are there and have decided they do not matter. It is not fine as a default, because the whole reason two versions of a document will not reconcile is usually sitting inside the thing you just told it to ignore.
Text out of a PDF needs one step first
Copy two PDFs and paste them here and almost every line will look changed, because a PDF puts a line break at the end of every visual line and those breaks fall in different places in the two versions. The text is the same; the wrapping is not.
Run both sides through remove line breaks first. It joins the wrapped lines, keeps the real paragraph breaks, and repairs the words split by a hyphen at the end of a line, which is what makes the comparison mean something.
Everything runs on your own machine. Nothing is uploaded, nothing is stored, and there is no account, so two drafts of a contract with real names and figures in them are safe to paste.
Common questions
These two lines look exactly the same. Why is it saying they are different?
Because one of them contains a character that renders the same as an ordinary one but is not it. A non-breaking space, a curly apostrophe, an en dash where you expected a hyphen, a zero-width character carried out of a web page, a tab standing in for spaces, or a trailing space nothing displays. This tool names which one it is and marks where it sits, rather than colouring the line red and leaving you to prove to yourself that they match.
Where do those invisible characters come from?
Word substitutes curly apostrophes and quotation marks as you type, and inserts a non-breaking space when it does not want a line to wrap. Copying out of a web page brings zero-width characters and non-breaking spaces with it. A PDF gives you soft hyphens. A keyboard set to a different layout gives you a different dash. None of them look wrong, which is exactly the problem.
Why does it show a whole paragraph as changed when I only altered one word?
It should not, and here it does not. Every edited line is compared again word by word, and only the words that actually moved are marked. Most comparison tools stop at the line, which on a forty-word clause leaves you doing the real work by eye.
I moved a paragraph and now the whole thing looks rewritten.
A plain comparison shows a move as a large deletion in one place and a large insertion in another, which reads as far more editing than actually happened. Here, a line that disappears from one place and reappears unchanged in another is reported as a move, with the line number it went to, so you can see nothing was edited.
What do the three tick boxes do?
They tell it what to treat as the same. Different capitals ignores case. Different spacing collapses runs of whitespace and ignores tabs, double spaces and trailing spaces, which also hides the invisible characters. Blank lines stops an added or removed empty line counting as a change. Leave them all off the first time, so you find out what is really in the text.
Do the line numbers still match my document?
Yes. They are the original line numbers from each side and they do not shift when blank lines are ignored, because you use them to find the line back in the document it came from. Renumbering would point you at the wrong place.
Can I compare two Word documents or two PDFs?
Not directly, but you can select all in each and paste. Text copied out of a PDF usually arrives wrapped at the column width with words split by hyphens, which makes almost every line look changed. Run both sides through the remove line breaks tool first and the comparison becomes readable.
What is "copy as a patch"?
A unified diff, the standard format for describing a change in text. It is what you paste into an email, a ticket or a message to say precisely what altered, and anyone technical will recognise it immediately.
Is either version of the text uploaded?
No. The comparison runs in your browser on your own machine, with no server and no account, and nothing is stored. Two versions of a contract, a policy or a tender are safe to paste.