Quick answer
Paste the original into box A and the edited version into box B: deletions are highlighted in red, additions in green, and inside changed lines the exact words that changed are marked. Compare by line (side by side or unified) or by word, optionally ignoring case or whitespace. The text is processed only in your browser.
What is a text compare (diff) tool?
A diff shows exactly what changed between two versions of a contract, an article, a quote or a piece of code, so you don't have to read them line by line. The tool uses the Myers algorithm, the same approach Git and most diff tools use, to find the smallest set of edits. Long unchanged stretches are collapsed so you can focus on the changes, and large texts are compared in a background thread so the page never freezes.
How to compare two texts
- 1
Paste the original into “Original (A)” and the new version into “Changed (B)”. Use “Swap A ↔ B” if you pasted them the wrong way round.
- 2
Choose “Compare by”: Lines (contracts, lists, code) or Words (flowing paragraphs).
- 3
When comparing by lines, pick “Side by side” or “Unified”. Tick “Ignore upper / lower case” or “Ignore whitespace differences” if you only care about the content.
- 4
Read the result: red means removed from A, green means added in B. The summary line counts added, removed and changed lines and words.
- 5
Click “⋯ n unchanged lines” to expand a collapsed section, or “Copy diff” to get a plain-text +/− version for an email or a note.
Picking the right comparison
| Mode | Best for | Examples |
|---|---|---|
| Lines, side by side | Line-based text you want to read in parallel | Contracts, clauses, lists, source code, config files |
| Lines, unified | Narrow screens, reading like a change log | Checking on a phone, sharing with a colleague |
| Words | Long paragraphs with few line breaks | Articles, emails, edited product descriptions |
| Ignore case | Content matters, capitalisation doesn't | Two hand-typed lists of names |
| Ignore whitespace | Indentation or stray spaces changed | Reformatted code, text pasted from Word |
Examples
Checking a contract that came back
Paste the version you sent into A and the returned one into B: “Price 100,000” changed to “Price 120,000” shows up as a changed line with only the number highlighted, so silent edits don't slip through.
Comparing two quotes
Compare by lines with “Ignore whitespace” so spaces copied from Excel don't add noise; the summary shows how many lines were added or removed.
Editing an article
Compare by words to see exactly which words an editor added or cut in each paragraph, without Word's track changes.
Finding a changed setting
Two config files thousands of lines long: unchanged stretches collapse, leaving only a few lines of context around each change.
Common problems
- Everything is highlighted even though only a few words changed.
- Usually the line breaks differ (one version wrapped, the other on one line). Compare by words, or enable “Ignore whitespace differences”.
- It says the texts differ too much.
- Above 6,000 edits the tool stops so your browser doesn't hang. Compare smaller parts or switch to comparing by lines.
- Accented letters look the same but are marked as different.
- One version may use decomposed Unicode (common when copying from PDFs). Normalise both with the Case Converter in “Keep as is” mode, then compare again.
- I want to compare two Word or PDF files.
- Open each file, select all, copy the text and paste it into the two boxes; formatting such as bold or tables isn't compared.
How the differences are found
The Myers algorithm (1986) finds the shortest way to turn A into B using insertions and deletions, treating each line (or word) as one unit. Identical text at the start and end is trimmed first to speed things up.
When comparing by lines, adjacent “delete then insert” blocks are paired into changed lines and compared again word by word, so you see the exact words that changed instead of a whole line in colour.
- Under 20,000 characters in total: compared instantly as you type.
- Longer: compared in a Web Worker (background thread) so the page stays responsive.
- More than 6,000 edits: the tool stops and tells you, rather than freezing the browser.
Glossary
- Diff
- The result of comparing two versions, listing what was added, removed or kept.
- Side by side
- Version A on the left and B on the right, with matching lines aligned.
- Unified
- A single column where removed lines start with − and added lines with +.
- Myers algorithm
- An algorithm that finds the minimum number of edits between two sequences, used by Git and many diff tools.
Frequently asked questions
Is my text uploaded?
No. The comparison runs entirely in your browser, so it's fine for contracts and internal documents.
How long can the texts be?
Tens of thousands of lines work on an ordinary computer; the practical limit is the number of differences (6,000), not the length.
Can I compare two files?
The tool compares text: open the files, copy their contents and paste them in. Plain text, CSV and source code paste most accurately.
What do red and green mean?
Red: present in the original A but removed in B. Green: present in the new B but not in A.
Why use “Ignore whitespace”?
Lines that only differ by indentation, extra spaces or tabs are treated as identical, leaving only real content changes.
Ratings and comments
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