Diff Checker — Compare Two Texts and Find Every Difference
Paste or open two versions and see what changed, highlighted word by word.
🔒 Runs in your browser — files never uploaded ⚡ No signup 💯 Free
Paste two versions of anything — a contract, an essay, a config file, a block of code — or open them from files, and see exactly what changed. Changed lines are paired up and the words that differ are highlighted inside them, so a one-character edit in a long paragraph is easy to spot. Read it side by side or inline, hide the unchanged parts, and copy the result as a standard patch.
Everything runs in your browser. Nothing is uploaded, which matters when the text is a production config or an unsigned agreement.
How to use Diff Checker
- Paste the original on the left and the changed version on the right — or click "Open file", or drop a file onto either box.
- Click Compare (or press Ctrl+Enter). After that the result updates as you edit.
- Read the result: red is removed, green is added, and the exact words that changed are highlighted more strongly.
- Tick Only show changed lines for long files, switch between side-by-side and inline view, or Copy as patch to share the changes.
Reading the comparison
Every line is matched against the other version with a longest-common-subsequence diff, the same idea behind git diff, so unchanged blocks stay aligned even after lines are inserted or deleted. Where a line was edited rather than added or removed, the old and new versions sit side by side, and a second, word-level comparison highlights exactly which words changed. Line numbers on both sides let you jump to the change in your own editor, and the counters above the result summarise the whole comparison.
Side by side or inline
Side by side is easiest to read on a wide screen. Inline shows each removed line (−) directly above its replacement (+), one column wide, which suits phones and long lines. "Auto" picks inline on narrow screens and side by side on wide ones.
Ignoring what does not matter
- Ignore trailing whitespace (on by default) hides the noise from editors that add or strip spaces at line ends. Turn it off where trailing spaces matter, such as Markdown line breaks.
- Ignore all whitespace treats "a = b" and "a=b" as the same, which is useful for re-indented code or reflowed text.
- Ignore case for comparing text where capitalisation changed but the words did not.
Long files: only the changes
For a long document with a few edits, tick "Only show changed lines". Each change keeps three lines of context, and the unchanged stretches between them collapse into a bar you can click to expand. Common lines at the start and end of the two texts are matched before the main comparison, so even two 20,000-line files with a handful of edits compare almost instantly.
Copy as patch
"Copy as patch" produces a standard unified diff (the --- / +++ / @@ format) that patch, git apply and code review tools understand. It is a compact way to send someone exactly what changed.
What people use it for
- Checking what changed between two drafts of a contract, policy or essay before signing or submitting.
- Comparing configuration files between two servers, or before and after an update.
- Reviewing code without a version control system to hand.
- Comparing two lists, two exports or two API responses to find the line that differs.
Frequently asked questions
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser — pasted text and opened files never leave your device.
Does it show which words changed inside a line?
Yes. Edited lines are paired, and the words that differ are highlighted in stronger red and green inside them, so small edits in long lines stand out.
Can I compare two files?
Yes. Click "Open file" above either box, or drag a file onto it. Any plain-text file works: .txt, .csv, .json, .xml, .html, code, configs. Word and PDF files need converting to text first.
Does it work on a phone?
Yes. On narrow screens the result switches to the inline view, one column with removed lines above added ones, so nothing is squeezed.
How large a text can I compare?
Up to 20,000 lines per side. Files that mostly match compare quickly at that size; two large texts that differ almost everywhere can hit the browser's memory limit, and the tool will say so.
How do I use the patch it copies?
Save it to a file and run patch original.txt changes.diff, or git apply changes.diff in a repository. It is the standard unified diff format with three lines of context.
Why is a line shown as removed and added instead of changed?
When a block of lines is replaced by a different number of lines, they are paired in order and any extra lines are shown as purely added or removed. If whitespace or capitalisation is the only difference, tick the matching "Ignore" option.