Text Diff Checker
Compare two blocks of text line by line and see exactly what was added, removed, or unchanged. Diffing runs in your browser; nothing is uploaded.
Private by construction. The conversion happens in this page's JavaScript. Nothing you paste here leaves your machine, and the tool keeps working with the network unplugged.
Paste the original on the left and the changed version on the right, and get a unified diff: unchanged lines indented, removed lines marked -, added lines marked +, with a summary count on top. The comparison uses a longest-common-subsequence algorithm — the same family of algorithm behind git diff — so a paragraph inserted in the middle shows up as an insertion, not as a wall of false changes. Diff tools are exactly where private text ends up: contracts before and after redlining, config files from two environments, essay drafts. This one never transmits either side anywhere.
Questions this tool gets asked
How does the comparison work?
Line by line, using a longest-common-subsequence algorithm. It finds the largest set of lines the two texts share in order, and reports everything else as an addition or removal - the same approach version-control diffs use.
Can it compare word-by-word instead of line-by-line?
Not yet. Line diffs are the reliable workhorse for code, configs, and prose with line breaks. For prose in one long paragraph, split it into sentences per line first and the diff becomes readable.
Is there a size limit?
Identical leading and trailing lines are skipped for free, then up to 2000 differing lines per side are compared. That covers configs and documents; for giant files, diff them in sections.
Which side is which in the output?
Lines starting with - exist only in the left (original) text; lines starting with + exist only in the right (changed) text. Indented lines appear in both.