About the Diff Checker
Tezmy's Diff Checker shows you exactly what changed between two versions of a text. Paste the original on the left and the new version on the right, press Compare, and changed lines are lined up side by side with the exact words that were added or removed highlighted. It uses the same kind of algorithm as Git, works for documents, contracts, essays, code, configuration files and lists, and can ignore differences in capital letters or spacing. Everything runs in your browser, so confidential text stays private.
Updated October 2026
How to use the Diff Checker
- 1Paste the original text on the left.
- 2Paste the changed version on the right.
- 3Press Compare.
- 4Review red (removed) and green (added) lines and words.
What people compare
- Two versions of a contract, to see exactly what the other side changed.
- An essay or article before and after editing.
- Code, configuration files and JSON before and after a change.
- Two lists, like last month's and this month's email or product lists.
- Translations and copy for websites and apps.
Reading the results
Lines only in the original are marked as removed and lines only in the new version as added, side by side with line numbers for both. Inside changed lines, the exact words that differ are highlighted, so a single changed number in a long paragraph is easy to spot. Unchanged lines stay plain, so your eye goes straight to what matters.
Ignore small differences
Tick ignore case to treat “Price” and “price” as the same, or ignore spaces to skip extra spaces and indentation changes. This is useful for code that was reformatted, or text copied from different places where only the spacing changed.
Compare Word and PDF documents
Open each document, select all the text and copy it, then paste the versions into the two boxes. For PDFs, extract the text first with PDF to Text. Formatting like bold and fonts isn't compared, only the words themselves.
Private comparisons
Contracts, reports and source code often contain confidential information. Here the comparison runs in your own browser, so neither version is uploaded or saved anywhere. Open this page in Safari, Chrome or Edge on your phone, tablet or computer. There's nothing to install and no sign-up, and everything runs on your own device, so what you type is never uploaded. After you compare two versions, count what changed with the Word Counter, or tidy a pasted data file with the JSON Formatter before you check it.
Features
- Side-by-side comparison
- Word-level highlights inside changed lines
- Line numbers for both versions
- Ignore case or extra spaces
- Works for text and code
- Private: nothing is uploaded
Frequently asked questions
How does the diff checker work?
It finds the smallest set of line changes that turns the original into the new text (the Myers diff algorithm, also used by Git), then compares changed lines word by word.
What do the colours mean?
Red shows text that was in the original but removed. Green shows text that was added in the new version. Unchanged lines have no colour.
Can I compare code?
Yes. It compares any plain text, including code, JSON, CSV and config files. Tick “Ignore extra spaces” to skip indentation changes.
Can I compare Word or PDF documents?
Copy the text out of each document and paste it in. Formatting like bold or fonts isn't compared, only the words.
Is my text stored or uploaded?
No. The comparison happens entirely in your browser.
Is there a size limit?
No fixed limit. Very long texts with thousands of lines take a moment longer to compare on older phones.
Can I compare two lists to find missing items?
Yes. Paste each list, one item per line. Removed lines show items missing from the new list, and added lines show new items. Sorting both lists first with Remove Duplicate Lines makes the comparison cleaner.
Does it work on my phone?
Yes, it works in any mobile browser. On small screens, the two versions are stacked so they stay readable.