Text Diff Checker
A text diff checker compares two versions of the same writing and marks exactly what changed between them — added lines in green, removed lines in red, and modified lines with the specific words that differ highlighted inside them. The ZTools Text Diff Checker runs a real line-level longest-common-subsequence pass and then a word-level pass inside each modified line, so a one-word edit in a long paragraph shows as one word changed, not the whole line rewritten. It offers a unified view and a side-by-side view, optional ignore-case and ignore-whitespace matching, and export of a patch-style unified diff. Everything runs in your browser via a useMemo/useDeferredValue pipeline — no text is uploaded, no CDN is called, and typing stays responsive on large inputs. It is built for prose and plain text — drafts, essays, translations, contract redlines, config files — where you care about wording rather than code review workflows.
Use cases
Comparing two drafts of a document
Paste yesterday's draft on the left and today's on the right to see every sentence you added, cut, or reworded. Word-level highlighting means a single reworded phrase stands out instead of the whole paragraph turning red, so you can review the actual edits at a glance before sending the newer version on.
Checking what an editor or collaborator changed
When a document comes back from a co-author or an editor, drop the original and the returned copy in to surface every silent change. This catches edits that a "track changes" pass missed — reordered lines, a swapped number, a quietly deleted clause — without needing the file to be in any particular format.
Reviewing a translation against its source revision
Compare two revisions of a translated text to confirm that a source-text update was actually carried through. Ignore-whitespace matching keeps reflowed line breaks from showing as false changes, so you only see the wording that genuinely moved.
Diffing config or note files without git
For a plain-text config, an .env sketch, or a set of meeting notes that is not under version control, paste the two states to get a clean unified diff you can copy into a ticket or a message — a lightweight stand-in for git diff when the file never lived in a repository.
How it works
- Paste the original text — Put the earlier version in the left (or top) panel. There is no length field to configure — the tool sizes itself to whatever you paste.
- Paste the changed text — Put the newer version in the right (or bottom) panel. The diff recomputes automatically as you type or paste; there is no "compare" button to wait on.
- Choose unified or side-by-side — Switch views with the segmented control. Unified stacks changes in one column; side-by-side aligns the two versions row-for-row for line-by-line reading.
- Tune the matching — Toggle ignore-case and ignore-whitespace when trivial differences (capitalisation, trailing spaces, reflowed breaks) are adding noise you do not care about.
- Read the highlighted result — Additions, deletions, and modifications are colour-coded, with the exact changed words marked inside modified lines. A running count summarises how many lines were added, removed, and changed.
- Copy or download the diff — Export a patch-style unified diff to paste into a ticket, a code review, or a message — the full result is always available even when only a capped number of rows is rendered on screen.
Examples
Input: Left: "Sugar is sweet" Right: "Honey is sweet"
Output: One modified line; the word "Sugar" marked removed and "Honey" marked added, the rest of the line unchanged.
Input: Left: 4 lines · Right: 5 lines (one line inserted in the middle)
Output: Four unchanged lines plus one green "added" line at the insertion point — not four "changed" lines below it.
Frequently asked questions
What is the difference between this and the Diff Checker?
They share the same underlying line-and-word diff engine. The Text Diff Checker is framed for prose and plain text — drafts, translations, notes, contract wording — while the Diff Checker leans toward code, JSON, and git-style review. Use whichever matches how you think about your comparison; the output is the same quality either way.
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser — nothing is sent to a server and no third-party script is loaded. You can disconnect from the internet and it still works.
Does word-level highlighting work inside long lines?
Yes. Within each modified line the tool runs a second, word-level pass, so a single reworded word in a long paragraph is highlighted on its own rather than marking the entire line as changed.
Can I ignore capitalisation or whitespace differences?
Yes. Ignore-case and ignore-whitespace toggles let you suppress differences you do not care about, which is useful for comparing text that was reflowed or re-cased without meaningful edits.
Can I export the result?
Yes — you can copy or download a patch-style unified diff. That format pastes cleanly into tickets, code reviews, and chat.
Is there a size limit?
There is no hard cap you configure. Very large inputs render a limited number of rows on screen for performance, but the complete diff is always available through copy and download.
Tips
- Turn on ignore-whitespace first when comparing text that was re-wrapped — it removes the most common source of false "changes".
- Use side-by-side view for reading two versions in parallel, and unified view for a compact change list to paste elsewhere.
- For a quick sanity check, load the built-in sample texts to see how additions, deletions, and word-level edits are rendered.
- Copy the unified diff into a ticket instead of screenshotting — reviewers can read the exact wording change rather than a picture of it.
Try it now
The full Text Diff Checker runs in your browser at https://ztools.zaions.com/text-diff — no signup, no upload, no data leaves your device.
Last updated: 2026-07-23 · Author: Ahsan Mahmood · Edit this page on GitHub