How to use the Text Diff
Last verified 2026-08-08 · about 5 minutes to read
The short version
- 1.Paste the original on the left. Any text works — code, prose, a CSV export, a log file.
- 2.Paste the changed version on the right. The comparison updates as you type. Nothing is uploaded.
- 3.Read the result. Removed lines are marked with a minus, added lines with a plus. Colour is never the only signal.
Why this is worth getting right
Comparison uses a longest-common-subsequence diff, the same approach as git, so a line inserted near the top does not mark every line after it as changed. Identical prefixes and suffixes are trimmed first, which is what keeps large files fast: two 20,000-line files differing in ten places skip more than 99% of the work.
Method 1 — use the Text Diff on this site
The fastest route. It runs entirely in your browser, so nothing is uploaded and there is no queue to wait in. No account is needed and there is no daily limit.
- Paste the original on the left. Any text works — code, prose, a CSV export, a log file.
- Paste the changed version on the right. The comparison updates as you type. Nothing is uploaded.
- Read the result. Removed lines are marked with a minus, added lines with a plus. Colour is never the only signal.
Method 2 — do it without this site
Worth knowing, because a tool you cannot replace is a dependency rather than a convenience. Most tasks in the text division have a command-line or built-in equivalent; it is usually more setup and less convenient, but it works offline and it is scriptable, which matters once you are doing something a hundred times instead of once.
What this tool will not do
Every tool has an edge. These are ours for text diff, stated up front so you find out here rather than halfway through a deadline:
- Line-level only. A one-character edit reads as a delete plus an add.
- Beyond about 2,000 differing lines on each side the comparison falls back to a whole-block replacement to avoid freezing the tab.
- Not a merge tool — it shows differences, it does not resolve them.
Questions people ask
How does the comparison work?
It computes the longest common subsequence of the two line lists, which is the same algorithm family that git diff uses. That finds the minimal set of insertions and deletions, rather than reporting everything after the first change as different.
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser. That matters more here than on most tools, because people diff contracts, config files with credentials in them, and unreleased code.
How large can the two texts be?
Comfortably a few thousand lines each. Identical leading and trailing sections are trimmed before the comparison starts, so two 20,000-line files that differ in ten places compare almost instantly.
Does it show which characters changed within a line?
Not yet — this is a line-level diff. A line with one changed character shows as one removal and one addition. Word-level highlighting is on the roadmap.
Why do two lines that look identical show as different?
Almost always trailing whitespace, or a CRLF line ending meeting an LF one. Turn on "ignore leading and trailing spaces" to confirm; if the difference disappears, that was it.