Diff Checker — Compare Two Texts

A worked example

Paste «The quick brown fox jumped over the lazy dog near the river.» as the original and «The quick red fox leaped over the sleepy dog near the old river.» as the changed text (the built-in example does this for you). The diff marks *brown*→*red*, *jumped*→*leaped*, *lazy*→*sleepy* and the inserted *old* — four word-level changes in one short sentence, the same granularity you'd get from a code-review diff applied to prose.

Scanning a long document

For a full chapter or contract, don't try to eyeball the whole inline result at once — use «Copy diff summary» for the added/removed/changed counts first, then switch to the aligned side-by-side view to scan line by line; a line that's ONLY on one side is a pure insertion or deletion, easy to spot without reading every word. If the document is very long, compare it section by section (the diff runs per-paste, not per-file) — that keeps each comparison fast and each result easy to review.

Aligned vs inline — which view to use

Inline (the default) shows one flowing paragraph with additions and deletions marked in place — fastest for a short edit where you just want to see what changed. Aligned side-by-side puts the original and changed text in two columns, line by line — better for longer documents or when you need to reference «line 12 of the original» in a comment to a co-author. Neither view edits anything; both are read-only comparisons of what you pasted.

For editors and localizers

Comparing a translation against its source, or a copy-edited draft against the original, is the same word-level diff — paste the source as «original» and the translation or edit as «changed». Nothing you paste is uploaded, stored or logged; the comparison runs entirely in your browser. When you're done, send the changed version on to the Grammar Checker or Words for a quick review — no re-typing needed.

Send changed text to Grammar Checker

How does the comparison work?

The two texts are split into words and compared with a longest-common-subsequence algorithm — the same technique code-review tools use. Words only in the second text are highlighted as added, words only in the first as removed.

Is my text uploaded to a server?

No. Both texts are compared entirely in your browser with JavaScript. Nothing you paste is uploaded, stored or logged — you can even use the tool offline once the page has loaded.

What kinds of text can I compare?

Any plain text — essays, contracts, articles, translations, or two drafts of the same document. The diff is word-level, so it works in any language that separates words with spaces; for very long documents, compare section by section.

Which view should I use for a long document?

Inline is best for a short edit — one flowing paragraph with changes marked in place. Aligned side-by-side is better for long documents: two columns, line by line, so you can reference a specific line number. Both show the same diff; switching between them never re-runs the comparison.

Can I compare a translation against its source text?

Yes — the diff is word-level and works with any text that separates words with spaces, so pasting a source and its translation (or an edit and its original) works the same as comparing two English drafts. The comparison itself doesn't understand meaning across languages; it just shows which words match and which don't.