How does the diff decide lines changed?

It aligns matching lines and reports the rest as added or removed, in the classic diff style. Rewritten lines usually show as a removal plus an addition rather than a special "changed" marker.

Why does a tiny edit show the whole paragraph changed?

Because the diff is line-based: one changed character makes the whole line differ. Diffing on smaller units (split the paragraph into lines) gives a tighter result.

Does whitespace matter?

Yes — trailing spaces and line-ending differences (CRLF vs LF) count as changes and are a common source of "nothing changed but everything is red". Normalise line endings before comparing if that noise is not what you are hunting.

Does it compare words or lines?

Both, at different levels. Lines are aligned and classified as added, removed or changed, and changed lines get inline markers showing the exact spans inside them. That is why a one-word edit highlights the word rather than the whole paragraph.

Is anything uploaded to make the comparison?

No. Both texts stay in your browser and the diff is computed locally, which is the main reason to reach for a web diff tool instead of pasting proprietary config into some random site that offers the same feature.

Text diff — Guide

Compare two texts and see the differences between them.

What it is and when to use it

Paste two texts and see their differences side by side. The comparison runs in the Monaco diff editor — the same component that powers VS Code — so you get line alignment, inline highlighting of what actually changed inside a line, moved-block detection and familiar keyboard shortcuts, rather than a hand-rolled line-by-line equality check. It is the no-install way to compare config exports, log excerpts, two versions of a paragraph, or a proposed file against the one in production before you commit to either.

Compares two blocks of text line by line to see exactly what changed.

How to use it

Paste the original text on the left
Paste the new text on the right
Review the highlighted additions and removals

A worked example

Fill in sample text

First line
Second line
Third line

Copy this into the tool, or open Text diff

Things that trip people up

The two panes are read-only for comparison purposes; edit the source files, not the diff view, unless you intend the diff view to be your scratch space.
Because Monaco is a full editor component, this page loads more JavaScript than most tools here — expect a slower first paint on a weak connection.
Whitespace differences are shown, not ignored: a trailing space or a tab-versus-spaces change registers as a real difference.

Questions people ask

How does the diff decide lines changed?: It aligns matching lines and reports the rest as added or removed, in the classic diff style. Rewritten lines usually show as a removal plus an addition rather than a special "changed" marker.
Why does a tiny edit show the whole paragraph changed?: Because the diff is line-based: one changed character makes the whole line differ. Diffing on smaller units (split the paragraph into lines) gives a tighter result.
Does whitespace matter?: Yes — trailing spaces and line-ending differences (CRLF vs LF) count as changes and are a common source of "nothing changed but everything is red". Normalise line endings before comparing if that noise is not what you are hunting.
Does it compare words or lines?: Both, at different levels. Lines are aligned and classified as added, removed or changed, and changed lines get inline markers showing the exact spans inside them. That is why a one-word edit highlights the word rather than the whole paragraph.
Is anything uploaded to make the comparison?: No. Both texts stay in your browser and the diff is computed locally, which is the main reason to reach for a web diff tool instead of pasting proprietary config into some random site that offers the same feature.

Next steps

Open the Text diff tool

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