About Redline Pad

What it is

Redline Pad compares two versions of a piece of text and shows you what changed, marked the way anyone who works with legal text expects to see it: insertions underlined, deletions struck through in place rather than hidden or moved to a margin. Put the original on one side and the revised version on the other — pasted, or typed there — and the redline appears as you go.

It is built for the job that comes up several times a day and does not deserve a document-comparison workflow — a clause pasted out of an email, a paragraph somebody rewrote overnight, two versions of a definition that look identical until you read them twice. You want to know what moved, and you want to know now.

What it is not

It is not a document-comparison platform. It does not open Word files, does not produce a DOCX with tracked changes, does not keep a history of what you compared, and has nothing to say about a two-hundred-page agreement with numbering and cross-references and a styles sheet somebody spent a week on.

Word's own Compare, Litera, Draftable and the rest are good at exactly those things, and they are the right tool when the job is a whole document, a file format, or a round trip back into tracked changes. If that is what you are doing, use one of those. This tool is for the clause you have in front of you now.

How it works

Both versions are turned into a plain internal representation — paragraphs, headings, lists, tables, and marks like bold and italic — and compared word by word. That part is a settled problem: a shortest-edit algorithm marks the fewest words it can and is always right about them. It is the floor here rather than the answer, because the fewest marks and the clearest redline are not the same thing.

Most of the work sits on top of it, deciding where a change really begins and ends. An edit is moved to the sentence that actually arrived rather than a word into it, a rewrite split around some word both versions happened to share is put back together, a paragraph split or merged is read as that, and formatting that changed on text that did not becomes a change in its own right. None of this is visible when it works, which is the point of it.

Two rules constrain everything else. Your text is never rewritten: settings like Ignore spacing and Match case change a derived key used for the comparison, never the characters that get displayed or copied. And the same two inputs always produce the same redline, byte for byte, so a colleague running the same comparison sees the same thing you did.

Who made it

I trained and worked in private practice and now work in-house, and this was built for two things that come up constantly in both.

A clause comes back revised, and the full document-comparison workflow is overkill for the job of simply reading what changed. Or the change is mine: I have reworded a paragraph, or written up what sales or IT asked for, and I need to show people exactly what I am proposing before it goes anywhere — which is as often a Teams thread with colleagues as it is a reply to the other side.

Nothing I could find did either job in a form I was willing to paste confidential text into.

If something looks wrong, I would like to hear about it. There is a feedback form.

What it costs

Redline Pad is free to use. There is no paid tier waiting behind a limit, no trial that expires, and no point at which you are asked to pay for anything. This paragraph promised to speak first about any change to that, so here it is speaking.

There is a desktop application coming, and it will be paid. It is a separate program that does what this page has just spent several paragraphs explaining the browser cannot. It opens .docx and PDF files from your own disk, compares whole documents rather than a clause, and writes tracked changes back into the original file. The page about it says what it does and what it does not, and has a waiting list if you want to hear when it exists.

None of that is a change to this tool. The browser version stays free, permanently, with everything it does today: no feature waiting behind a payment, no setting locked, no limit that appears once you have used it enough. If you only ever want the thing you are reading about, nothing about it is going to start costing money.