This tool puts two versions of something side by side and marks what actually changed — the paragraph that was rewritten between drafts, the line that differs between two config files, the clause someone quietly edited in a contract. It compares line by line and shows added lines in green and removed ones in red, collapsing the long stretches that are identical so the changes are not buried. It can also ignore case and whitespace, which removes the noise when reindentation or a find-and-replace makes every line look different. Both texts stay in your browser.
No. The comparison runs entirely in your browser, so contracts, drafts and configuration files are safe to paste here.
Line by line. A line with a single changed word shows as one removal and one addition, which keeps long documents readable. For prose, breaking the text at sentences before comparing makes the result easier to follow.
Ignore whitespace collapses runs of spaces and tabs and trims the ends of lines, so reindented code compares as unchanged. Ignore case treats upper and lower case as the same. Both affect only the comparison — the text shown is always what you pasted.
Because a hundred unchanged lines around one edit make the edit harder to find. A few lines of context are kept around every change, and the rest is replaced with a note saying how many lines were collapsed.
Not directly — it compares plain text. Copy the text out of the documents and paste it in, or export both to plain text first. Formatting, images and layout are not part of the comparison.