Text Compare

How to use it

1. Paste the original version on the left and the newer one on the right.
2. The comparison appears underneath as you type. Removed text is red, added text is green, and a line that was edited shows both with only the changed words marked.
3. Use Show only differences on a long document to hide everything that stayed the same.

What the colours mean

• Red row — the line exists in the original and not in the new version. It was deleted.
• Green row — the line is new. Nothing corresponds to it on the left.
• Amber row — the line was edited. Both versions are shown, with the specific words that were removed highlighted in red on the left and the words that replaced them in green on the right.
• No colour — the line is identical in both.

An empty grey cell means that side has nothing at this point, which is how an insertion or deletion keeps the two columns lined up instead of everything below it drifting out of step.

How the comparison works

The two texts are aligned using Myers' diff algorithm — the same approach behind git diff. It finds the shortest set of edits that turns one text into the other, which matters more than it sounds: a naive line-by-line comparison that meets an inserted line will report every line after it as changed, because everything has shifted down by one. Myers finds the insert and keeps the rest aligned.

Once lines are aligned, any deletion sitting directly opposite an insertion is treated as an edit rather than two separate events, and the same algorithm runs again across the words of that line. That is why you see "three" highlighted rather than the whole sentence.

The ignore options

• Capitalisation — treats Hello and hello as the same line. Useful when one version has been through a system that upper-cases everything.
• Spacing and indentation — collapses runs of spaces and ignores leading and trailing whitespace, so a re-indented document does not show up as entirely rewritten.
• Blank lines — drops empty lines from both sides before comparing, which is the quickest way to cut through a reformatted document.

These affect only the comparison, never the display. The text shown is always exactly what you pasted, so you can see the capitalisation you told it to ignore.

Why it matters that this runs locally

Most online diff tools send both versions of your document to a server to be compared. For a code snippet that may not bother you. For a contract, a patient record, a legal draft or anything under an NDA, it means handing two complete copies of a confidential document to a third party you have no agreement with.

This tool does the comparison in your browser. There is no server to send anything to, and no request carries your text anywhere — you can watch the Network tab while you type, or disconnect from the internet and keep working. That is the whole reason to prefer it over the better-known alternatives.

What people use it for

Contract and policy revisions

Paste the version you signed and the version you were just sent. Word-level highlighting makes a changed figure or an inserted "not" obvious, which is exactly the kind of edit that is easy to miss reading two documents side by side.

Checking what an editor changed

Compare your draft against the returned copy to see every alteration, rather than taking a track-changes file on trust.

Configuration and data files

Two versions of a config, an export before and after a migration, or two lists that should match. Turn on Show only differences and the answer is usually two or three rows.

Questions

Is my text uploaded?

No. The diff is a JavaScript function running in your browser, and nothing you paste leaves the page. See our Privacy Policy for the full position.

How large a document can it handle?

Several thousand lines compare in well under a second. Two very large documents that share almost nothing are the expensive case for any diff algorithm, so there is a ceiling past which the tool reports a wholesale replacement rather than freezing your tab. You will not meet it with ordinary text.

Why is a moved paragraph shown as deleted and added?

Because that is what it is, as far as a line-based diff is concerned. Detecting that a block moved rather than being removed in one place and written in another is a genuinely harder problem, and tools that attempt it often guess wrong. This one reports what it can be sure of.

Can I compare files rather than pasted text?

Not yet — paste is the only input. Open the file, select all, paste. It keeps the tool honest about never touching your filesystem.

Does it work with code?

Yes. The comparison is plain text, so it works for any language, and Spacing and indentation is useful when only the formatting has changed. There is no syntax highlighting — this compares text rather than parsing it.