Text Diff Checker
Compare two blocks of text and highlight what was added or removed, line by line. Free and fully in-browser.
The quick brown fox−jumps over the lazy dog+leaps over the lazy catHello world+New line here
How to use the Text Diff Checker
- 1Paste your original text into the left input pane, either by copying from a document or typing directly.
- 2Paste the revised or updated version into the right input pane so the tool has both versions to compare.
- 3Click the Compare button to run the diff; the tool aligns the two texts and highlights the changes line by line.
- 4Read the results, where added lines appear in green, removed lines in red, and unchanged lines stay neutral for context.
- 5Optionally toggle whitespace handling or line normalization if invisible spaces or wrapping are causing false differences.
- 6Copy the highlighted output or the list of changes to share with a colleague, or edit either pane and re-run to refine the comparison.
About the Text Diff Checker
Text Diff Checker compares two blocks of text and shows you exactly what changed between them: which lines were added, which were removed, and which stayed the same. You paste an original version into the left pane and a revised version into the right pane, and the tool aligns the two side by side, marking additions in green and deletions in red so differences jump out at a glance.
Under the hood it runs a line-by-line comparison based on a longest-common-subsequence algorithm, the same core logic that powers version-control diffs like the ones you see in Git. It matches unchanged lines first, then reports the gaps between them as insertions or deletions. Everything happens inside your browser using JavaScript. Your text is never uploaded to a server, never logged, and never leaves your device, which makes it safe for confidential drafts, contracts, source code, or anything under an NDA.
Real uses are everywhere. Writers and editors compare two drafts of an article to see what a proofreader changed. Developers check two versions of a config file, a JSON payload, or a log snippet without opening a full IDE. Lawyers and students spot silent edits in contracts or essays. Support teams diff a working command against a broken one to find the typo. Translators verify that only the intended strings were touched.
A few practical tips: trim trailing whitespace before comparing if invisible spaces are throwing off the results, since a line that looks identical but has a stray tab will register as changed. For very long documents, comparing section by section keeps the highlighted output readable. If you only care about wording and not formatting, normalize line breaks first so wrapped paragraphs line up.
Why it matters: manually re-reading two nearly identical documents is slow and error-prone, and the human eye skips small changes like a flipped digit or a deleted "not." A structured diff catches those instantly. Because Text Diff Checker is free, requires no signup, and processes everything locally, you get that precision without sending sensitive material anywhere.
Frequently asked questions
Does the diff compare line by line or word by word?
The core comparison is line by line: each line in the original is matched against the revised text, and lines that do not match are shown as added or removed. This is ideal for code, config files, and structured text where each line is a meaningful unit. If a single word changes inside a line, that whole line is flagged as changed so you can see the surrounding context.
Why are two lines that look identical showing up as different?
Almost always it is invisible characters: trailing spaces, tabs versus spaces, or different line endings (Windows CRLF versus Unix LF). The comparison is exact, so a stray space at the end of a line counts as a real difference. Trim trailing whitespace or enable whitespace normalization before comparing to eliminate these false positives.
Is there a limit on how much text I can compare?
There is no fixed server limit because the comparison runs entirely in your browser. Practically, the constraint is your device's memory and how readable the highlighted output stays. Comparing tens of thousands of lines works, but for very large files it is faster and clearer to diff one section at a time.
Can I use this to compare code or JSON?
Yes. The tool treats input as plain text, so it works well for source code, JSON, YAML, CSV, and log files. It does not do language-aware syntax parsing, but for spotting which lines were added, removed, or edited between two versions it behaves just like a basic Git diff.
Is my text safe if I paste a confidential document?
Yes. All processing happens client-side in your browser using JavaScript. Your text is never sent to a server, stored, or logged, so nothing leaves your device. That makes it safe for contracts, private drafts, credentials, or anything covered by an NDA. You can even disconnect from the internet after the page loads and the comparison still works.
Related tools
Browse all free online tools in Text tools and more.
Frequently asked questions
Is my text private?+
Yes — the comparison runs entirely in your browser.