Text Diff Checker

A diff compares two versions of some text and shows you exactly what changed between them. This tool takes an original and a changed version, lines them up using a longest-common-subsequence algorithm, and marks each line as unchanged, added, or removed — added lines are highlighted green with a plus, removed lines red with a minus, and it reports how many lines were added and removed. It is the same idea behind the diffs you see in code review and version control, but for any text: paste two drafts of an email, two config files, or two copies of a document and instantly see what moved. Everything is computed in your browser, so it is fast and private.

This tool performs a line-level diff: it compares the two texts one whole line at a time, so a line is reported as either unchanged, added, or removed. If you edit a few words inside a line, that line shows up as one removal plus one addition rather than highlighting only the changed words. Line diffs are ideal for code, configuration files, logs, and structured text where each line is a meaningful unit, and they keep the output clean and easy to scan. A word-level or character-level diff highlights smaller in-line changes but is noisier; for most everyday comparisons the line view is clearer and is what version-control tools show by default.

Yes. The comparison runs entirely in your browser with JavaScript — neither block of text is sent to a server, logged, or stored, and there is no account or tracking of what you compare. That makes it safe to diff sensitive material like contracts, internal documents, configuration, or source code without uploading it anywhere. Because the work is local, the tool also keeps functioning offline once the page has loaded. Nothing about your input leaves your device, so you can paste freely and the only copy of your text is the one in front of you.

Anywhere you need to see what changed between two pieces of text. Common uses include comparing two drafts of an article or email to catch edits, checking two configuration or environment files for differences before a deploy, reviewing changes someone made to a document, comparing two log snapshots, or spotting what differs between two versions of a code snippet outside your editor. Paste the original on the left and the changed version on the right, press Compare, and the added and removed lines are highlighted with counts. Use Swap to flip which side is treated as the original, and Clear to start over.

No — the comparison is exact, so two lines must match character for character to count as unchanged. That means differences in capitalization, leading or trailing spaces, indentation, and tabs versus spaces will show up as changes. This is deliberate: for code and config those differences often matter, and hiding them could mask a real change. If you want to ignore such differences, normalize both sides first — for example lower-case everything or trim trailing spaces in your editor — and then paste them in. Trailing blank lines are tolerated, but otherwise what you paste is compared as-is.