Free tool
Diff Checker: Compare Text by Line, Word or Letter and Merge Changes
Paste an original and a changed version, press Compare, and every difference is marked in place. You can ignore case or spacing, jump between changes, merge a block either way and save the result as a standard diff file.
Keys: Cmd Enter compare, Option ↓ and ↑ next and previous change. On Windows use Ctrl and Alt.
Both texts are compared in your browser and are never uploaded or stored. Only your view and precision settings are remembered on this device.
When you have two versions and no idea what changed
A client sends back edited copy, a config file behaves differently on two servers, or a contract came back after review. Put the first version in Original and the second in Changed. You can type, paste, or use Open file on either side, and Swap sides flips them if you loaded them the wrong way round.
Press Compare, or Cmd or Ctrl with Enter. After the first comparison the result keeps following your edits, so you can fix a text and watch the differences shrink.
Choosing how much detail to see
| Setting | What it does |
|---|---|
| Line | Marks whole lines that were added, removed or changed |
| Word | Inside a changed line, marks the words that differ |
| Letter | Inside a changed line, marks the exact characters, useful for typos |
| Side by side | Two columns, original left and changed right |
| One column | A single stream, like a patch |
| Only changes | Folds the lines that did not change |
The summary above the result counts how many lines were added and removed, so you can judge the size of the edit at a glance.
Ignoring noise
- Ignore case treats Hello and hello as the same.
- Ignore spaces stops changes in spacing from showing as edits.
- Ignore blank lines hides empty lines that were added or removed.
These are useful when one text was reformatted and you only care about the words. Turn them off again before you export, if the exact spacing matters for the file you are checking.
Merging, moving between changes and exporting
Each block of changes has buttons that take the original's lines into the changed text, or the changed lines into the original. Undo merge reverses the last merge. The up and down arrows, or Option with the arrow keys on a Mac and Alt on Windows, move to the previous and next change.
Download .diff saves the differences as a unified diff, the plain text patch format that code tools understand, and Copy diff puts it on the clipboard. The sides can also be saved back as text files with their own Save buttons.
A review routine for edited copy
- Paste the approved text in Original and the edited text in Changed.
- Start with Word precision and Only changes switched on.
- Step through each change with the arrow buttons.
- Merge the edits you accept, and leave the ones you do not.
- Copy the merged text from the Changed side.
This keeps a proofreading round short, because you only read the parts that moved instead of the whole document again.
For code or config files, switch to Letter precision when a line looks identical but is flagged, because a single swapped character or a trailing space is often the cause. Download .diff afterwards if a developer needs the change as a patch, and keep the original file untouched until the merge has been checked.
What it can and cannot tell you
The tool compares characters of text. It does not understand meaning, so a paragraph moved to another place shows as a removal and an addition. It also works on text, so a Word file or a PDF needs to be pasted as text first.
It helps when you review a page before and after an edit, such as the copy on a site after a redesign. Our Webflow maintenance page describes how we handle ongoing changes.
Frequently asked questions
How does the comparison work?
It finds the shortest set of line changes between the two texts, then compares inside the changed lines by word or by letter, depending on your choice.
Can I compare two files?
Yes. Use Open file on each side. Text files work best, and you can also drop a file onto a box.
What is a unified diff?
It is a plain text format that lists removed lines with a minus and added lines with a plus, with some surrounding lines for context. Many code tools can apply it.
Can I undo a merge?
Yes. Undo merge steps back through the merges you made.
Does it ignore line endings or trailing spaces?
The Ignore spaces switch hides differences in spacing. For other cases, compare as they are and look at the marked lines.
Are my texts uploaded?
No. They stay in this browser tab and are not remembered when you close it.
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