NNonkera

Text Diff Checker

Productivity

Paste two versions of text side by side and see exactly which lines were added, removed, or changed — compared entirely in your browser.

How the comparison works

This tool compares two blocks of text line by line and highlights what's different between them: lines only present in the original are marked as removed, lines only present in the new version are marked as added, and lines that match are shown unchanged. It uses a standard longest-common-subsequence approach — the same underlying idea behind the diff view in Git and most version control tools — to line up the two texts as closely as possible before flagging the differences, rather than naively comparing line 1 to line 1, line 2 to line 2, and so on, which would falsely flag every line as changed after a single inserted line.

Why use a diff checker

Reading two similar documents side by side and spotting every small change by eye is slow and error-prone, especially once a document is more than a paragraph or two — a single word changed mid-sentence, or one line quietly deleted, is easy to miss when scanning manually. A diff checker does that comparison mechanically and precisely, so nothing gets overlooked, and it turns a tedious side-by-side read-through into a quick glance at exactly what moved.

Common use cases

Writers and editors use it to compare draft revisions and see exactly what an editor changed, without relying on tracked-changes markup from a specific word processor. Developers use it to compare two versions of a config file, a snippet of code, or plain-text data outside of a full version-control diff. Students and researchers use it to check how much a paraphrased passage actually differs from the original, and legal and contract reviewers use it to catch subtle wording changes between two versions of an agreement that might otherwise slip past a manual read-through.

Reading the diff output

Removed lines (present only in the original) and added lines (present only in the new version) are color-coded so the change is visible at a glance without reading every word of unchanged surrounding text. Because the comparison works line by line, a single word changed in the middle of a sentence shows that whole line as both removed (the old version) and added (the new version) rather than highlighting just the one word — which is normal behavior for a line-based diff and mirrors how most code diff tools work too.

Limitations to know about

This is a line-based comparison, so reordering paragraphs without changing their content will show up as removals and additions rather than a "moved" indicator, and differences in trailing whitespace or line breaks can occasionally cause a line to be flagged as changed even when the visible text looks identical. If you're specifically comparing paragraph structure rather than wording, it can help to strip extra blank lines from both texts before pasting them in, so the comparison lines up cleanly.

How to use Text Diff Checker

  1. 1Paste the original text on the left.
  2. 2Paste the updated text on the right.
  3. 3Review the highlighted additions and removals.

Frequently asked questions

Does this compare word by word or line by line?

Line by line — each line of the original is matched against the new version, and lines that don't match are marked as added or removed.

Is my text uploaded anywhere?

No — the comparison runs entirely in your browser using JavaScript. Neither text you paste in is sent to a server.

Why does a single changed word mark the whole line as different?

Because the comparison works at the line level, any change within a line — even one word — causes that whole line to show as removed (old) and added (new), which is standard behavior for line-based diff tools.

Can I compare code with this tool?

Yes — it works on any plain text, including code, config files, or CSV data, though it isn't syntax-aware the way a dedicated code diff tool might be.

Does it detect moved paragraphs?

Not specifically — a moved block of text will typically show as a removal in its old position and an addition in its new one, rather than being flagged as "moved."

Is there a limit to how much text I can compare?

No hard limit, though very large documents (many thousands of lines) may take a moment longer to process since comparison happens on your device rather than a server.